timer file descriptor HOWTO

timer file descriptor HOWTO¶
- Release:
1.13
This HOWTO discusses Python’s support for the linux timer file descriptor.
Examples¶
The following example shows how to use a timer file descriptor to execute a function twice a second:
# Practical scripts should use really use a non-blocking timer,
# we use a blocking timer here for simplicity.
import os, time
# Create the timer file descriptor
fd = os.timerfd_create(time.CLOCK_REALTIME)
# Start the timer in 1 second, with an interval of half a second
os.timerfd_settime(fd, initial=1, interval=0.5)
try:
# Process timer events four times.
for _ in range(4):
# read() will block until the timer expires
_ = os.read(fd, 8)
print("Timer expired")
finally:
# Remember to close the timer file descriptor!
os.close(fd)
To avoid the precision loss caused by the float
type,
timer file descriptors allow specifying initial expiration and interval
in integer nanoseconds with _ns
variants of the functions.
This example shows how epoll()
can be used with timer file
descriptors to wait until the file descriptor is ready for reading:
import os, time, select, socket, sys
# Create an epoll object
ep = select.epoll()
# In this example, use loopback address to send "stop" command to the server.
#
# $ telnet 127.0.0.1 1234
# Trying 127.0.0.1...
# Connected to 127.0.0.1.
# Escape character is '^]'.
# stop
# Connection closed by foreign host.
#
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.bind(("127.0.0.1", 1234))
sock.setblocking(False)
sock.listen(1)
ep.register(sock, select.EPOLLIN)
# Create timer file descriptors in non-blocking mode.
num = 3
fds = []
for _ in range(num):
fd = os.timerfd_create(time.CLOCK_REALTIME, flags=os.TFD_NONBLOCK)
fds.append(fd)
# Register the timer file descriptor for read events
ep.register(fd, select.EPOLLIN)
# Start the timer with os.timerfd_settime_ns() in nanoseconds.
# Timer 1 fires every 0.25 seconds; timer 2 every 0.5 seconds; etc
for i, fd in enumerate(fds, start=1):
one_sec_in_nsec = 10**9
i = i * one_sec_in_nsec
os.timerfd_settime_ns(fd, initial=i//4, interval=i//4)
timeout = 3
try:
conn = None
is_active = True
while is_active:
# Wait for the timer to expire for 3 seconds.
# epoll.poll() returns a list of (fd, event) pairs.
# fd is a file descriptor.
# sock and conn[=returned value of socket.accept()] are socket objects, not file descriptors.
# So use sock.fileno() and conn.fileno() to get the file descriptors.
events = ep.poll(timeout)
# If more than one timer file descriptors are ready for reading at once,
# epoll.poll() returns a list of (fd, event) pairs.
#
# In this example settings,
# 1st timer fires every 0.25 seconds in 0.25 seconds. (0.25, 0.5, 0.75, 1.0, ...)
# 2nd timer every 0.5 seconds in 0.5 seconds. (0.5, 1.0, 1.5, 2.0, ...)
# 3rd timer every 0.75 seconds in 0.75 seconds. (0.75, 1.5, 2.25, 3.0, ...)
#
# In 0.25 seconds, only 1st timer fires.
# In 0.5 seconds, 1st timer and 2nd timer fires at once.
# In 0.75 seconds, 1st timer and 3rd timer fires at once.
# In 1.5 seconds, 1st timer, 2nd timer and 3rd timer fires at once.
#
# If a timer file descriptor is signaled more than once since
# the last os.read() call, os.read() returns the number of signaled
# as host order of class bytes.
print(f"Signaled events={events}")
for fd, event in events:
if event & select.EPOLLIN:
if fd == sock.fileno():
# Check if there is a connection request.
print(f"Accepting connection {fd}")
conn, addr = sock.accept()
conn.setblocking(False)
print(f"Accepted connection {conn} from {addr}")
ep.register(conn, select.EPOLLIN)
elif conn and fd == conn.fileno():
# Check if there is data to read.
print(f"Reading data {fd}")
data = conn.recv(1024)
if data:
# You should catch UnicodeDecodeError exception for safety.
cmd = data.decode()
if cmd.startswith("stop"):
print(f"Stopping server")
is_active = False
else:
print(f"Unknown command: {cmd}")
else:
# No more data, close connection
print(f"Closing connection {fd}")
ep.unregister(conn)
conn.close()
conn = None
elif fd in fds:
print(f"Reading timer {fd}")
count = int.from_bytes(os.read(fd, 8), byteorder=sys.byteorder)
print(f"Timer {fds.index(fd) + 1} expired {count} times")
else:
print(f"Unknown file descriptor {fd}")
finally:
for fd in fds:
ep.unregister(fd)
os.close(fd)
ep.close()
This example shows how select()
can be used with timer file
descriptors to wait until the file descriptor is ready for reading:
import os, time, select, socket, sys
# In this example, use loopback address to send "stop" command to the server.
#
# $ telnet 127.0.0.1 1234
# Trying 127.0.0.1...
# Connected to 127.0.0.1.
# Escape character is '^]'.
# stop
# Connection closed by foreign host.
#
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.bind(("127.0.0.1", 1234))
sock.setblocking(False)
sock.listen(1)
# Create timer file descriptors in non-blocking mode.
num = 3
fds = [os.timerfd_create(time.CLOCK_REALTIME, flags=os.TFD_NONBLOCK)
for _ in range(num)]
select_fds = fds + [sock]
# Start the timers with os.timerfd_settime() in seconds.
# Timer 1 fires every 0.25 seconds; timer 2 every 0.5 seconds; etc
for i, fd in enumerate(fds, start=1):
os.timerfd_settime(fd, initial=i/4, interval=i/4)
timeout = 3
try:
conn = None
is_active = True
while is_active:
# Wait for the timer to expire for 3 seconds.
# select.select() returns a list of file descriptors or objects.
rfd, wfd, xfd = select.select(select_fds, select_fds, select_fds, timeout)
for fd in rfd:
if fd == sock:
# Check if there is a connection request.
print(f"Accepting connection {fd}")
conn, addr = sock.accept()
conn.setblocking(False)
print(f"Accepted connection {conn} from {addr}")
select_fds.append(conn)
elif conn and fd == conn:
# Check if there is data to read.
print(f"Reading data {fd}")
data = conn.recv(1024)
if data:
# You should catch UnicodeDecodeError exception for safety.
cmd = data.decode()
if cmd.startswith("stop"):
print(f"Stopping server")
is_active = False
else:
print(f"Unknown command: {cmd}")
else:
# No more data, close connection
print(f"Closing connection {fd}")
select_fds.remove(conn)
conn.close()
conn = None
elif fd in fds:
print(f"Reading timer {fd}")
count = int.from_bytes(os.read(fd, 8), byteorder=sys.byteorder)
print(f"Timer {fds.index(fd) + 1} expired {count} times")
else:
print(f"Unknown file descriptor {fd}")
finally:
for fd in fds:
os.close(fd)
sock.close()
sock = None


Unicode Objects and Codecs

Unicode Objects and Codecs¶
Unicode Objects¶
Since the implementation of PEP 393 in Python 3.3, Unicode objects internally use a variety of representations, in order to allow handling the complete range of Unicode characters while staying memory efficient. There are special cases for strings where all code points are below 128, 256, or 65536; otherwise, code points must be below 1114112 (which is the full Unicode range).
UTF-8 representation is created on demand and cached in the Unicode object.
Note
The Py_UNICODE
representation has been removed since Python 3.12
with deprecated APIs.
See PEP 623 for more information.
Unicode Type¶
These are the basic Unicode object types used for the Unicode implementation in Python:
-
PyTypeObject PyUnicode_Type¶
- Part of the Stable ABI.
This instance of
PyTypeObject
represents the Python Unicode type. It is exposed to Python code asstr
.
-
PyTypeObject PyUnicodeIter_Type¶
- Part of the Stable ABI.
This instance of
PyTypeObject
represents the Python Unicode iterator type. It is used to iterate over Unicode string objects.
-
type Py_UCS4¶
-
type Py_UCS2¶
-
type Py_UCS1¶
- Part of the Stable ABI.
These types are typedefs for unsigned integer types wide enough to contain characters of 32 bits, 16 bits and 8 bits, respectively. When dealing with single Unicode characters, use
Py_UCS4
.Added in version 3.3.
-
type PyASCIIObject¶
-
type PyCompactUnicodeObject¶
-
type PyUnicodeObject¶
These subtypes of
PyObject
represent a Python Unicode object. In almost all cases, they shouldn’t be used directly, since all API functions that deal with Unicode objects take and returnPyObject
pointers.Added in version 3.3.
The structure of a particular object can be determined using the following macros. The macros cannot fail; their behavior is undefined if their argument is not a Python Unicode object.
-
PyUnicode_IS_COMPACT(o)¶
True if o uses the
PyCompactUnicodeObject
structure.Added in version 3.3.
-
PyUnicode_IS_COMPACT_ASCII(o)¶
True if o uses the
PyASCIIObject
structure.Added in version 3.3.
-
PyUnicode_IS_COMPACT(o)¶
The following APIs are C macros and static inlined functions for fast checks and access to internal read-only data of Unicode objects:
-
int PyUnicode_Check(PyObject *obj)¶
Return true if the object obj is a Unicode object or an instance of a Unicode subtype. This function always succeeds.
-
int PyUnicode_CheckExact(PyObject *obj)¶
Return true if the object obj is a Unicode object, but not an instance of a subtype. This function always succeeds.
-
Py_ssize_t PyUnicode_GET_LENGTH(PyObject *unicode)¶
Return the length of the Unicode string, in code points. unicode has to be a Unicode object in the “canonical” representation (not checked).
Added in version 3.3.
-
Py_UCS1 *PyUnicode_1BYTE_DATA(PyObject *unicode)¶
-
Py_UCS2 *PyUnicode_2BYTE_DATA(PyObject *unicode)¶
-
Py_UCS4 *PyUnicode_4BYTE_DATA(PyObject *unicode)¶
Return a pointer to the canonical representation cast to UCS1, UCS2 or UCS4 integer types for direct character access. No checks are performed if the canonical representation has the correct character size; use
PyUnicode_KIND()
to select the right function.Added in version 3.3.
-
PyUnicode_1BYTE_KIND¶
-
PyUnicode_2BYTE_KIND¶
-
PyUnicode_4BYTE_KIND¶
Return values of the
PyUnicode_KIND()
macro.Added in version 3.3.
Changed in version 3.12:
PyUnicode_WCHAR_KIND
has been removed.
-
int PyUnicode_KIND(PyObject *unicode)¶
Return one of the PyUnicode kind constants (see above) that indicate how many bytes per character this Unicode object uses to store its data. unicode has to be a Unicode object in the “canonical” representation (not checked).
Added in version 3.3.
-
void *PyUnicode_DATA(PyObject *unicode)¶
Return a void pointer to the raw Unicode buffer. unicode has to be a Unicode object in the “canonical” representation (not checked).
Added in version 3.3.
-
void PyUnicode_WRITE(int kind, void *data, Py_ssize_t index, Py_UCS4 value)¶
Write the code point value to the given zero-based index in a string.
The kind value and data pointer must have been obtained from a string using
PyUnicode_KIND()
andPyUnicode_DATA()
respectively. You must hold a reference to that string while callingPyUnicode_WRITE()
. All requirements ofPyUnicode_WriteChar()
also apply.The function performs no checks for any of its requirements, and is intended for usage in loops.
Added in version 3.3.
-
Py_UCS4 PyUnicode_READ(int kind, void *data, Py_ssize_t index)¶
Read a code point from a canonical representation data (as obtained with
PyUnicode_DATA()
). No checks or ready calls are performed.Added in version 3.3.
-
Py_UCS4 PyUnicode_READ_CHAR(PyObject *unicode, Py_ssize_t index)¶
Read a character from a Unicode object unicode, which must be in the “canonical” representation. This is less efficient than
PyUnicode_READ()
if you do multiple consecutive reads.Added in version 3.3.
-
Py_UCS4 PyUnicode_MAX_CHAR_VALUE(PyObject *unicode)¶
Return the maximum code point that is suitable for creating another string based on unicode, which must be in the “canonical” representation. This is always an approximation but more efficient than iterating over the string.
Added in version 3.3.
-
int PyUnicode_IsIdentifier(PyObject *unicode)¶
- Part of the Stable ABI.
Return
1
if the string is a valid identifier according to the language definition, section Names (identifiers and keywords). Return0
otherwise.Changed in version 3.9: The function does not call
Py_FatalError()
anymore if the string is not ready.
-
unsigned int PyUnicode_IS_ASCII(PyObject *unicode)¶
Return true if the string only contains ASCII characters. Equivalent to
str.isascii()
.Added in version 3.2.
Unicode Character Properties¶
Unicode provides many different character properties. The most often needed ones are available through these macros which are mapped to C functions depending on the Python configuration.
-
int Py_UNICODE_ISSPACE(Py_UCS4 ch)¶
Return
1
or0
depending on whether ch is a whitespace character.
-
int Py_UNICODE_ISUPPER(Py_UCS4 ch)¶
Return
1
or0
depending on whether ch is an uppercase character.
-
int Py_UNICODE_ISLINEBREAK(Py_UCS4 ch)¶
Return
1
or0
depending on whether ch is a linebreak character.
-
int Py_UNICODE_ISALPHA(Py_UCS4 ch)¶
Return
1
or0
depending on whether ch is an alphabetic character.
-
int Py_UNICODE_ISALNUM(Py_UCS4 ch)¶
Return
1
or0
depending on whether ch is an alphanumeric character.
-
int Py_UNICODE_ISPRINTABLE(Py_UCS4 ch)¶
Return
1
or0
depending on whether ch is a printable character, in the sense ofstr.isprintable()
.
These APIs can be used for fast direct character conversions:
-
int Py_UNICODE_TODECIMAL(Py_UCS4 ch)¶
Return the character ch converted to a decimal positive integer. Return
-1
if this is not possible. This function does not raise exceptions.
-
int Py_UNICODE_TODIGIT(Py_UCS4 ch)¶
Return the character ch converted to a single digit integer. Return
-1
if this is not possible. This function does not raise exceptions.
-
double Py_UNICODE_TONUMERIC(Py_UCS4 ch)¶
Return the character ch converted to a double. Return
-1.0
if this is not possible. This function does not raise exceptions.
These APIs can be used to work with surrogates:
-
int Py_UNICODE_IS_HIGH_SURROGATE(Py_UCS4 ch)¶
Check if ch is a high surrogate (
0xD800 <= ch <= 0xDBFF
).
-
int Py_UNICODE_IS_LOW_SURROGATE(Py_UCS4 ch)¶
Check if ch is a low surrogate (
0xDC00 <= ch <= 0xDFFF
).
-
Py_UCS4 Py_UNICODE_HIGH_SURROGATE(Py_UCS4 ch)¶
Return the high UTF-16 surrogate (
0xD800
to0xDBFF
) for a Unicode code point in the range[0x10000; 0x10FFFF]
.
-
Py_UCS4 Py_UNICODE_LOW_SURROGATE(Py_UCS4 ch)¶
Return the low UTF-16 surrogate (
0xDC00
to0xDFFF
) for a Unicode code point in the range[0x10000; 0x10FFFF]
.
-
Py_UCS4 Py_UNICODE_JOIN_SURROGATES(Py_UCS4 high, Py_UCS4 low)¶
Join two surrogate code points and return a single
Py_UCS4
value. high and low are respectively the leading and trailing surrogates in a surrogate pair. high must be in the range[0xD800; 0xDBFF]
and low must be in the range[0xDC00; 0xDFFF]
.
Creating and accessing Unicode strings¶
To create Unicode objects and access their basic sequence properties, use these APIs:
-
PyObject *PyUnicode_New(Py_ssize_t size, Py_UCS4 maxchar)¶
- Return value: New reference.
Create a new Unicode object. maxchar should be the true maximum code point to be placed in the string. As an approximation, it can be rounded up to the nearest value in the sequence 127, 255, 65535, 1114111.
On error, set an exception and return
NULL
.After creation, the string can be filled by
PyUnicode_WriteChar()
,PyUnicode_CopyCharacters()
,PyUnicode_Fill()
,PyUnicode_WRITE()
or similar. Since strings are supposed to be immutable, take care to not “use” the result while it is being modified. In particular, before it’s filled with its final contents, a string:must not be hashed,
must not be
converted to UTF-8
, or another non-“canonical” representation,must not have its reference count changed,
must not be shared with code that might do one of the above.
This list is not exhaustive. Avoiding these uses is your responsibility; Python does not always check these requirements.
To avoid accidentally exposing a partially-written string object, prefer using the
PyUnicodeWriter
API, or one of thePyUnicode_From*
functions below.Added in version 3.3.
-
PyObject *PyUnicode_FromKindAndData(int kind, const void *buffer, Py_ssize_t size)¶
- Return value: New reference.
Create a new Unicode object with the given kind (possible values are
PyUnicode_1BYTE_KIND
etc., as returned byPyUnicode_KIND()
). The buffer must point to an array of size units of 1, 2 or 4 bytes per character, as given by the kind.If necessary, the input buffer is copied and transformed into the canonical representation. For example, if the buffer is a UCS4 string (
PyUnicode_4BYTE_KIND
) and it consists only of codepoints in the UCS1 range, it will be transformed into UCS1 (PyUnicode_1BYTE_KIND
).Added in version 3.3.
-
PyObject *PyUnicode_FromStringAndSize(const char *str, Py_ssize_t size)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object from the char buffer str. The bytes will be interpreted as being UTF-8 encoded. The buffer is copied into the new object. The return value might be a shared object, i.e. modification of the data is not allowed.
This function raises
SystemError
when:size < 0,
str is
NULL
and size > 0
Changed in version 3.12: str ==
NULL
with size > 0 is not allowed anymore.
-
PyObject *PyUnicode_FromString(const char *str)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object from a UTF-8 encoded null-terminated char buffer str.
-
PyObject *PyUnicode_FromFormat(const char *format, ...)¶
- Return value: New reference. Part of the Stable ABI.
Take a C
printf()
-style format string and a variable number of arguments, calculate the size of the resulting Python Unicode string and return a string with the values formatted into it. The variable arguments must be C types and must correspond exactly to the format characters in the format ASCII-encoded string.A conversion specifier contains two or more characters and has the following components, which must occur in this order:
The
'%'
character, which marks the start of the specifier.Conversion flags (optional), which affect the result of some conversion types.
Minimum field width (optional). If specified as an
'*'
(asterisk), the actual width is given in the next argument, which must be of type int, and the object to convert comes after the minimum field width and optional precision.Precision (optional), given as a
'.'
(dot) followed by the precision. If specified as'*'
(an asterisk), the actual precision is given in the next argument, which must be of type int, and the value to convert comes after the precision.Length modifier (optional).
Conversion type.
The conversion flag characters are:
Flag
Meaning
0
The conversion will be zero padded for numeric values.
-
The converted value is left adjusted (overrides the
0
flag if both are given).The length modifiers for following integer conversions (
d
,i
,o
,u
,x
, orX
) specify the type of the argument (int by default):Modifier
Types
l
long or unsigned long
ll
long long or unsigned long long
j
intmax_t
oruintmax_t
z
size_t
orssize_t
t
ptrdiff_t
The length modifier
l
for following conversionss
orV
specify that the type of the argument is const wchar_t*.The conversion specifiers are:
Conversion Specifier
Type
Comment
%
n/a
The literal
%
character.d
,i
Specified by the length modifier
The decimal representation of a signed C integer.
u
Specified by the length modifier
The decimal representation of an unsigned C integer.
o
Specified by the length modifier
The octal representation of an unsigned C integer.
x
Specified by the length modifier
The hexadecimal representation of an unsigned C integer (lowercase).
X
Specified by the length modifier
The hexadecimal representation of an unsigned C integer (uppercase).
c
int
A single character.
s
const char* or const wchar_t*
A null-terminated C character array.
p
const void*
The hex representation of a C pointer. Mostly equivalent to
printf("%p")
except that it is guaranteed to start with the literal0x
regardless of what the platform’sprintf
yields.A
The result of calling
ascii()
.U
A Unicode object.
V
PyObject*, const char* or const wchar_t*
A Unicode object (which may be
NULL
) and a null-terminated C character array as a second parameter (which will be used, if the first parameter isNULL
).S
The result of calling
PyObject_Str()
.R
The result of calling
PyObject_Repr()
.T
Get the fully qualified name of an object type; call
PyType_GetFullyQualifiedName()
.#T
Similar to
T
format, but use a colon (:
) as separator between the module name and the qualified name.N
Get the fully qualified name of a type; call
PyType_GetFullyQualifiedName()
.#N
Similar to
N
format, but use a colon (:
) as separator between the module name and the qualified name.Note
The width formatter unit is number of characters rather than bytes. The precision formatter unit is number of bytes or
wchar_t
items (if the length modifierl
is used) for"%s"
and"%V"
(if thePyObject*
argument isNULL
), and a number of characters for"%A"
,"%U"
,"%S"
,"%R"
and"%V"
(if thePyObject*
argument is notNULL
).Note
Unlike to C
printf()
the0
flag has effect even when a precision is given for integer conversions (d
,i
,u
,o
,x
, orX
).Changed in version 3.2: Support for
"%lld"
and"%llu"
added.Changed in version 3.3: Support for
"%li"
,"%lli"
and"%zi"
added.Changed in version 3.4: Support width and precision formatter for
"%s"
,"%A"
,"%U"
,"%V"
,"%S"
,"%R"
added.Changed in version 3.12: Support for conversion specifiers
o
andX
. Support for length modifiersj
andt
. Length modifiers are now applied to all integer conversions. Length modifierl
is now applied to conversion specifierss
andV
. Support for variable width and precision*
. Support for flag-
.An unrecognized format character now sets a
SystemError
. In previous versions it caused all the rest of the format string to be copied as-is to the result string, and any extra arguments discarded.Changed in version 3.13: Support for
%T
,%#T
,%N
and%#N
formats added.
-
PyObject *PyUnicode_FromFormatV(const char *format, va_list vargs)¶
- Return value: New reference. Part of the Stable ABI.
Identical to
PyUnicode_FromFormat()
except that it takes exactly two arguments.
-
PyObject *PyUnicode_FromObject(PyObject *obj)¶
- Return value: New reference. Part of the Stable ABI.
Copy an instance of a Unicode subtype to a new true Unicode object if necessary. If obj is already a true Unicode object (not a subtype), return a new strong reference to the object.
Objects other than Unicode or its subtypes will cause a
TypeError
.
-
PyObject *PyUnicode_FromOrdinal(int ordinal)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode Object from the given Unicode code point ordinal.
The ordinal must be in
range(0x110000)
. AValueError
is raised in the case it is not.
-
PyObject *PyUnicode_FromEncodedObject(PyObject *obj, const char *encoding, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Decode an encoded object obj to a Unicode object.
bytes
,bytearray
and other bytes-like objects are decoded according to the given encoding and using the error handling defined by errors. Both can beNULL
to have the interface use the default values (see Built-in Codecs for details).All other objects, including Unicode objects, cause a
TypeError
to be set.The API returns
NULL
if there was an error. The caller is responsible for decref’ing the returned objects.
-
void PyUnicode_Append(PyObject **p_left, PyObject *right)¶
- Part of the Stable ABI.
Append the string right to the end of p_left. p_left must point to a strong reference to a Unicode object;
PyUnicode_Append()
releases (“steals”) this reference.On error, set *p_left to
NULL
and set an exception.On success, set *p_left to a new strong reference to the result.
-
void PyUnicode_AppendAndDel(PyObject **p_left, PyObject *right)¶
- Part of the Stable ABI.
The function is similar to
PyUnicode_Append()
, with the only difference being that it decrements the reference count of right by one.
-
PyObject *PyUnicode_BuildEncodingMap(PyObject *string)¶
- Return value: New reference. Part of the Stable ABI.
Return a mapping suitable for decoding a custom single-byte encoding. Given a Unicode string string of up to 256 characters representing an encoding table, returns either a compact internal mapping object or a dictionary mapping character ordinals to byte values. Raises a
TypeError
and returnNULL
on invalid input.Added in version 3.2.
-
const char *PyUnicode_GetDefaultEncoding(void)¶
- Part of the Stable ABI.
Return the name of the default string encoding,
"utf-8"
. Seesys.getdefaultencoding()
.The returned string does not need to be freed, and is valid until interpreter shutdown.
-
Py_ssize_t PyUnicode_GetLength(PyObject *unicode)¶
- Part of the Stable ABI since version 3.7.
Return the length of the Unicode object, in code points.
On error, set an exception and return
-1
.Added in version 3.3.
-
Py_ssize_t PyUnicode_CopyCharacters(PyObject *to, Py_ssize_t to_start, PyObject *from, Py_ssize_t from_start, Py_ssize_t how_many)¶
Copy characters from one Unicode object into another. This function performs character conversion when necessary and falls back to
memcpy()
if possible. Returns-1
and sets an exception on error, otherwise returns the number of copied characters.The string must not have been “used” yet. See
PyUnicode_New()
for details.Added in version 3.3.
-
int PyUnicode_Resize(PyObject **unicode, Py_ssize_t length);¶
- Part of the Stable ABI.
Resize a Unicode object *unicode to the new length in code points.
Try to resize the string in place (which is usually faster than allocating a new string and copying characters), or create a new string.
*unicode is modified to point to the new (resized) object and
0
is returned on success. Otherwise,-1
is returned and an exception is set, and *unicode is left untouched.The function doesn’t check string content, the result may not be a string in canonical representation.
-
Py_ssize_t PyUnicode_Fill(PyObject *unicode, Py_ssize_t start, Py_ssize_t length, Py_UCS4 fill_char)¶
Fill a string with a character: write fill_char into
unicode[start:start+length]
.Fail if fill_char is bigger than the string maximum character, or if the string has more than 1 reference.
The string must not have been “used” yet. See
PyUnicode_New()
for details.Return the number of written character, or return
-1
and raise an exception on error.Added in version 3.3.
-
int PyUnicode_WriteChar(PyObject *unicode, Py_ssize_t index, Py_UCS4 character)¶
- Part of the Stable ABI since version 3.7.
Write a character to the string unicode at the zero-based index. Return
0
on success,-1
on error with an exception set.This function checks that unicode is a Unicode object, that the index is not out of bounds, and that the object’s reference count is one. See
PyUnicode_WRITE()
for a version that skips these checks, making them your responsibility.The string must not have been “used” yet. See
PyUnicode_New()
for details.Added in version 3.3.
-
Py_UCS4 PyUnicode_ReadChar(PyObject *unicode, Py_ssize_t index)¶
- Part of the Stable ABI since version 3.7.
Read a character from a string. This function checks that unicode is a Unicode object and the index is not out of bounds, in contrast to
PyUnicode_READ_CHAR()
, which performs no error checking.Return character on success,
-1
on error with an exception set.Added in version 3.3.
-
PyObject *PyUnicode_Substring(PyObject *unicode, Py_ssize_t start, Py_ssize_t end)¶
- Return value: New reference. Part of the Stable ABI since version 3.7.
Return a substring of unicode, from character index start (included) to character index end (excluded). Negative indices are not supported. On error, set an exception and return
NULL
.Added in version 3.3.
-
Py_UCS4 *PyUnicode_AsUCS4(PyObject *unicode, Py_UCS4 *buffer, Py_ssize_t buflen, int copy_null)¶
- Part of the Stable ABI since version 3.7.
Copy the string unicode into a UCS4 buffer, including a null character, if copy_null is set. Returns
NULL
and sets an exception on error (in particular, aSystemError
if buflen is smaller than the length of unicode). buffer is returned on success.Added in version 3.3.
-
Py_UCS4 *PyUnicode_AsUCS4Copy(PyObject *unicode)¶
- Part of the Stable ABI since version 3.7.
Copy the string unicode into a new UCS4 buffer that is allocated using
PyMem_Malloc()
. If this fails,NULL
is returned with aMemoryError
set. The returned buffer always has an extra null code point appended.Added in version 3.3.
Locale Encoding¶
The current locale encoding can be used to decode text from the operating system.
-
PyObject *PyUnicode_DecodeLocaleAndSize(const char *str, Py_ssize_t length, const char *errors)¶
- Return value: New reference. Part of the Stable ABI since version 3.7.
Decode a string from UTF-8 on Android and VxWorks, or from the current locale encoding on other platforms. The supported error handlers are
"strict"
and"surrogateescape"
(PEP 383). The decoder uses"strict"
error handler if errors isNULL
. str must end with a null character but cannot contain embedded null characters.Use
PyUnicode_DecodeFSDefaultAndSize()
to decode a string from the filesystem encoding and error handler.This function ignores the Python UTF-8 Mode.
See also
The
Py_DecodeLocale()
function.Added in version 3.3.
Changed in version 3.7: The function now also uses the current locale encoding for the
surrogateescape
error handler, except on Android. Previously,Py_DecodeLocale()
was used for thesurrogateescape
, and the current locale encoding was used forstrict
.
-
PyObject *PyUnicode_DecodeLocale(const char *str, const char *errors)¶
- Return value: New reference. Part of the Stable ABI since version 3.7.
Similar to
PyUnicode_DecodeLocaleAndSize()
, but compute the string length usingstrlen()
.Added in version 3.3.
-
PyObject *PyUnicode_EncodeLocale(PyObject *unicode, const char *errors)¶
- Return value: New reference. Part of the Stable ABI since version 3.7.
Encode a Unicode object to UTF-8 on Android and VxWorks, or to the current locale encoding on other platforms. The supported error handlers are
"strict"
and"surrogateescape"
(PEP 383). The encoder uses"strict"
error handler if errors isNULL
. Return abytes
object. unicode cannot contain embedded null characters.Use
PyUnicode_EncodeFSDefault()
to encode a string to the filesystem encoding and error handler.This function ignores the Python UTF-8 Mode.
See also
The
Py_EncodeLocale()
function.Added in version 3.3.
Changed in version 3.7: The function now also uses the current locale encoding for the
surrogateescape
error handler, except on Android. Previously,Py_EncodeLocale()
was used for thesurrogateescape
, and the current locale encoding was used forstrict
.
File System Encoding¶
Functions encoding to and decoding from the filesystem encoding and error handler (PEP 383 and PEP 529).
To encode file names to bytes
during argument parsing, the "O&"
converter should be used, passing PyUnicode_FSConverter()
as the
conversion function:
-
int PyUnicode_FSConverter(PyObject *obj, void *result)¶
- Part of the Stable ABI.
PyArg_Parse* converter: encode
str
objects – obtained directly or through theos.PathLike
interface – tobytes
usingPyUnicode_EncodeFSDefault()
;bytes
objects are output as-is. result must be an address of a C variable of type PyObject* (or PyBytesObject*). On success, set the variable to a new strong reference to a bytes object which must be released when it is no longer used and return a non-zero value (Py_CLEANUP_SUPPORTED
). Embedded null bytes are not allowed in the result. On failure, return0
with an exception set.If obj is
NULL
, the function releases a strong reference stored in the variable referred by result and returns1
.Added in version 3.1.
Changed in version 3.6: Accepts a path-like object.
To decode file names to str
during argument parsing, the "O&"
converter should be used, passing PyUnicode_FSDecoder()
as the
conversion function:
-
int PyUnicode_FSDecoder(PyObject *obj, void *result)¶
- Part of the Stable ABI.
PyArg_Parse* converter: decode
bytes
objects – obtained either directly or indirectly through theos.PathLike
interface – tostr
usingPyUnicode_DecodeFSDefaultAndSize()
;str
objects are output as-is. result must be an address of a C variable of type PyObject* (or PyUnicodeObject*). On success, set the variable to a new strong reference to a Unicode object which must be released when it is no longer used and return a non-zero value (Py_CLEANUP_SUPPORTED
). Embedded null characters are not allowed in the result. On failure, return0
with an exception set.If obj is
NULL
, release the strong reference to the object referred to by result and return1
.Added in version 3.2.
Changed in version 3.6: Accepts a path-like object.
-
PyObject *PyUnicode_DecodeFSDefaultAndSize(const char *str, Py_ssize_t size)¶
- Return value: New reference. Part of the Stable ABI.
Decode a string from the filesystem encoding and error handler.
If you need to decode a string from the current locale encoding, use
PyUnicode_DecodeLocaleAndSize()
.See also
The
Py_DecodeLocale()
function.Changed in version 3.6: The filesystem error handler is now used.
-
PyObject *PyUnicode_DecodeFSDefault(const char *str)¶
- Return value: New reference. Part of the Stable ABI.
Decode a null-terminated string from the filesystem encoding and error handler.
If the string length is known, use
PyUnicode_DecodeFSDefaultAndSize()
.Changed in version 3.6: The filesystem error handler is now used.
-
PyObject *PyUnicode_EncodeFSDefault(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object to the filesystem encoding and error handler, and return
bytes
. Note that the resultingbytes
object can contain null bytes.If you need to encode a string to the current locale encoding, use
PyUnicode_EncodeLocale()
.See also
The
Py_EncodeLocale()
function.Added in version 3.2.
Changed in version 3.6: The filesystem error handler is now used.
wchar_t Support¶
wchar_t
support for platforms which support it:
-
PyObject *PyUnicode_FromWideChar(const wchar_t *wstr, Py_ssize_t size)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object from the
wchar_t
buffer wstr of the given size. Passing-1
as the size indicates that the function must itself compute the length, usingwcslen()
. ReturnNULL
on failure.
-
Py_ssize_t PyUnicode_AsWideChar(PyObject *unicode, wchar_t *wstr, Py_ssize_t size)¶
- Part of the Stable ABI.
Copy the Unicode object contents into the
wchar_t
buffer wstr. At most sizewchar_t
characters are copied (excluding a possibly trailing null termination character). Return the number ofwchar_t
characters copied or-1
in case of an error.When wstr is
NULL
, instead return the size that would be required to store all of unicode including a terminating null.Note that the resulting wchar_t* string may or may not be null-terminated. It is the responsibility of the caller to make sure that the wchar_t* string is null-terminated in case this is required by the application. Also, note that the wchar_t* string might contain null characters, which would cause the string to be truncated when used with most C functions.
-
wchar_t *PyUnicode_AsWideCharString(PyObject *unicode, Py_ssize_t *size)¶
- Part of the Stable ABI since version 3.7.
Convert the Unicode object to a wide character string. The output string always ends with a null character. If size is not
NULL
, write the number of wide characters (excluding the trailing null termination character) into *size. Note that the resultingwchar_t
string might contain null characters, which would cause the string to be truncated when used with most C functions. If size isNULL
and the wchar_t* string contains null characters aValueError
is raised.Returns a buffer allocated by
PyMem_New
(usePyMem_Free()
to free it) on success. On error, returnsNULL
and *size is undefined. Raises aMemoryError
if memory allocation is failed.Added in version 3.2.
Changed in version 3.7: Raises a
ValueError
if size isNULL
and the wchar_t* string contains null characters.
Built-in Codecs¶
Python provides a set of built-in codecs which are written in C for speed. All of these codecs are directly usable via the following functions.
Many of the following APIs take two arguments encoding and errors, and they
have the same semantics as the ones of the built-in str()
string object
constructor.
Setting encoding to NULL
causes the default encoding to be used
which is UTF-8. The file system calls should use
PyUnicode_FSConverter()
for encoding file names. This uses the
filesystem encoding and error handler internally.
Error handling is set by errors which may also be set to NULL
meaning to use
the default handling defined for the codec. Default error handling for all
built-in codecs is “strict” (ValueError
is raised).
The codecs all use a similar interface. Only deviations from the following generic ones are documented for simplicity.
Generic Codecs¶
The following macro is provided:
-
Py_UNICODE_REPLACEMENT_CHARACTER¶
The Unicode code point
U+FFFD
(replacement character).This Unicode character is used as the replacement character during decoding if the errors argument is set to “replace”.
These are the generic codec APIs:
-
PyObject *PyUnicode_Decode(const char *str, Py_ssize_t size, const char *encoding, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the encoded string str. encoding and errors have the same meaning as the parameters of the same name in the
str()
built-in function. The codec to be used is looked up using the Python codec registry. ReturnNULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_AsEncodedString(PyObject *unicode, const char *encoding, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object and return the result as Python bytes object. encoding and errors have the same meaning as the parameters of the same name in the Unicode
encode()
method. The codec to be used is looked up using the Python codec registry. ReturnNULL
if an exception was raised by the codec.
UTF-8 Codecs¶
These are the UTF-8 codec APIs:
-
PyObject *PyUnicode_DecodeUTF8(const char *str, Py_ssize_t size, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the UTF-8 encoded string str. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_DecodeUTF8Stateful(const char *str, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)¶
- Return value: New reference. Part of the Stable ABI.
If consumed is
NULL
, behave likePyUnicode_DecodeUTF8()
. If consumed is notNULL
, trailing incomplete UTF-8 byte sequences will not be treated as an error. Those bytes will not be decoded and the number of bytes that have been decoded will be stored in consumed.
-
PyObject *PyUnicode_AsUTF8String(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object using UTF-8 and return the result as Python bytes object. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.The function fails if the string contains surrogate code points (
U+D800
-U+DFFF
).
-
const char *PyUnicode_AsUTF8AndSize(PyObject *unicode, Py_ssize_t *size)¶
- Part of the Stable ABI since version 3.10.
Return a pointer to the UTF-8 encoding of the Unicode object, and store the size of the encoded representation (in bytes) in size. The size argument can be
NULL
; in this case no size will be stored. The returned buffer always has an extra null byte appended (not included in size), regardless of whether there are any other null code points.On error, set an exception, set size to
-1
(if it’s not NULL) and returnNULL
.The function fails if the string contains surrogate code points (
U+D800
-U+DFFF
).This caches the UTF-8 representation of the string in the Unicode object, and subsequent calls will return a pointer to the same buffer. The caller is not responsible for deallocating the buffer. The buffer is deallocated and pointers to it become invalid when the Unicode object is garbage collected.
Added in version 3.3.
Changed in version 3.7: The return type is now
const char *
rather ofchar *
.Changed in version 3.10: This function is a part of the limited API.
-
const char *PyUnicode_AsUTF8(PyObject *unicode)¶
As
PyUnicode_AsUTF8AndSize()
, but does not store the size.Warning
This function does not have any special behavior for null characters embedded within unicode. As a result, strings containing null characters will remain in the returned string, which some C functions might interpret as the end of the string, leading to truncation. If truncation is an issue, it is recommended to use
PyUnicode_AsUTF8AndSize()
instead.Added in version 3.3.
Changed in version 3.7: The return type is now
const char *
rather ofchar *
.
UTF-32 Codecs¶
These are the UTF-32 codec APIs:
-
PyObject *PyUnicode_DecodeUTF32(const char *str, Py_ssize_t size, const char *errors, int *byteorder)¶
- Return value: New reference. Part of the Stable ABI.
Decode size bytes from a UTF-32 encoded buffer string and return the corresponding Unicode object. errors (if non-
NULL
) defines the error handling. It defaults to “strict”.If byteorder is non-
NULL
, the decoder starts decoding using the given byte order:*byteorder == -1: little endian *byteorder == 0: native order *byteorder == 1: big endian
If
*byteorder
is zero, and the first four bytes of the input data are a byte order mark (BOM), the decoder switches to this byte order and the BOM is not copied into the resulting Unicode string. If*byteorder
is-1
or1
, any byte order mark is copied to the output.After completion, *byteorder is set to the current byte order at the end of input data.
If byteorder is
NULL
, the codec starts in native order mode.Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_DecodeUTF32Stateful(const char *str, Py_ssize_t size, const char *errors, int *byteorder, Py_ssize_t *consumed)¶
- Return value: New reference. Part of the Stable ABI.
If consumed is
NULL
, behave likePyUnicode_DecodeUTF32()
. If consumed is notNULL
,PyUnicode_DecodeUTF32Stateful()
will not treat trailing incomplete UTF-32 byte sequences (such as a number of bytes not divisible by four) as an error. Those bytes will not be decoded and the number of bytes that have been decoded will be stored in consumed.
-
PyObject *PyUnicode_AsUTF32String(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Return a Python byte string using the UTF-32 encoding in native byte order. The string always starts with a BOM mark. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.
UTF-16 Codecs¶
These are the UTF-16 codec APIs:
-
PyObject *PyUnicode_DecodeUTF16(const char *str, Py_ssize_t size, const char *errors, int *byteorder)¶
- Return value: New reference. Part of the Stable ABI.
Decode size bytes from a UTF-16 encoded buffer string and return the corresponding Unicode object. errors (if non-
NULL
) defines the error handling. It defaults to “strict”.If byteorder is non-
NULL
, the decoder starts decoding using the given byte order:*byteorder == -1: little endian *byteorder == 0: native order *byteorder == 1: big endian
If
*byteorder
is zero, and the first two bytes of the input data are a byte order mark (BOM), the decoder switches to this byte order and the BOM is not copied into the resulting Unicode string. If*byteorder
is-1
or1
, any byte order mark is copied to the output (where it will result in either a\ufeff
or a\ufffe
character).After completion,
*byteorder
is set to the current byte order at the end of input data.If byteorder is
NULL
, the codec starts in native order mode.Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_DecodeUTF16Stateful(const char *str, Py_ssize_t size, const char *errors, int *byteorder, Py_ssize_t *consumed)¶
- Return value: New reference. Part of the Stable ABI.
If consumed is
NULL
, behave likePyUnicode_DecodeUTF16()
. If consumed is notNULL
,PyUnicode_DecodeUTF16Stateful()
will not treat trailing incomplete UTF-16 byte sequences (such as an odd number of bytes or a split surrogate pair) as an error. Those bytes will not be decoded and the number of bytes that have been decoded will be stored in consumed.
-
PyObject *PyUnicode_AsUTF16String(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Return a Python byte string using the UTF-16 encoding in native byte order. The string always starts with a BOM mark. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.
UTF-7 Codecs¶
These are the UTF-7 codec APIs:
-
PyObject *PyUnicode_DecodeUTF7(const char *str, Py_ssize_t size, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the UTF-7 encoded string str. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_DecodeUTF7Stateful(const char *str, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)¶
- Return value: New reference. Part of the Stable ABI.
If consumed is
NULL
, behave likePyUnicode_DecodeUTF7()
. If consumed is notNULL
, trailing incomplete UTF-7 base-64 sections will not be treated as an error. Those bytes will not be decoded and the number of bytes that have been decoded will be stored in consumed.
Unicode-Escape Codecs¶
These are the “Unicode Escape” codec APIs:
-
PyObject *PyUnicode_DecodeUnicodeEscape(const char *str, Py_ssize_t size, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the Unicode-Escape encoded string str. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_AsUnicodeEscapeString(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object using Unicode-Escape and return the result as a bytes object. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.
Raw-Unicode-Escape Codecs¶
These are the “Raw Unicode Escape” codec APIs:
-
PyObject *PyUnicode_DecodeRawUnicodeEscape(const char *str, Py_ssize_t size, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the Raw-Unicode-Escape encoded string str. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_AsRawUnicodeEscapeString(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object using Raw-Unicode-Escape and return the result as a bytes object. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.
Latin-1 Codecs¶
These are the Latin-1 codec APIs: Latin-1 corresponds to the first 256 Unicode ordinals and only these are accepted by the codecs during encoding.
-
PyObject *PyUnicode_DecodeLatin1(const char *str, Py_ssize_t size, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the Latin-1 encoded string str. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_AsLatin1String(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object using Latin-1 and return the result as Python bytes object. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.
ASCII Codecs¶
These are the ASCII codec APIs. Only 7-bit ASCII data is accepted. All other codes generate errors.
-
PyObject *PyUnicode_DecodeASCII(const char *str, Py_ssize_t size, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the ASCII encoded string str. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_AsASCIIString(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object using ASCII and return the result as Python bytes object. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.
Character Map Codecs¶
This codec is special in that it can be used to implement many different codecs
(and this is in fact what was done to obtain most of the standard codecs
included in the encodings
package). The codec uses mappings to encode and
decode characters. The mapping objects provided must support the
__getitem__()
mapping interface; dictionaries and sequences work well.
These are the mapping codec APIs:
-
PyObject *PyUnicode_DecodeCharmap(const char *str, Py_ssize_t length, PyObject *mapping, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Create a Unicode object by decoding size bytes of the encoded string str using the given mapping object. Return
NULL
if an exception was raised by the codec.If mapping is
NULL
, Latin-1 decoding will be applied. Else mapping must map bytes ordinals (integers in the range from 0 to 255) to Unicode strings, integers (which are then interpreted as Unicode ordinals) orNone
. Unmapped data bytes – ones which cause aLookupError
, as well as ones which get mapped toNone
,0xFFFE
or'\ufffe'
, are treated as undefined mappings and cause an error.
-
PyObject *PyUnicode_AsCharmapString(PyObject *unicode, PyObject *mapping)¶
- Return value: New reference. Part of the Stable ABI.
Encode a Unicode object using the given mapping object and return the result as a bytes object. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.The mapping object must map Unicode ordinal integers to bytes objects, integers in the range from 0 to 255 or
None
. Unmapped character ordinals (ones which cause aLookupError
) as well as mapped toNone
are treated as “undefined mapping” and cause an error.
The following codec API is special in that maps Unicode to Unicode.
-
PyObject *PyUnicode_Translate(PyObject *unicode, PyObject *table, const char *errors)¶
- Return value: New reference. Part of the Stable ABI.
Translate a string by applying a character mapping table to it and return the resulting Unicode object. Return
NULL
if an exception was raised by the codec.The mapping table must map Unicode ordinal integers to Unicode ordinal integers or
None
(causing deletion of the character).Mapping tables need only provide the
__getitem__()
interface; dictionaries and sequences work well. Unmapped character ordinals (ones which cause aLookupError
) are left untouched and are copied as-is.errors has the usual meaning for codecs. It may be
NULL
which indicates to use the default error handling.
MBCS codecs for Windows¶
These are the MBCS codec APIs. They are currently only available on Windows and use the Win32 MBCS converters to implement the conversions. Note that MBCS (or DBCS) is a class of encodings, not just one. The target encoding is defined by the user settings on the machine running the codec.
-
PyObject *PyUnicode_DecodeMBCS(const char *str, Py_ssize_t size, const char *errors)¶
- Return value: New reference. Part of the Stable ABI on Windows since version 3.7.
Create a Unicode object by decoding size bytes of the MBCS encoded string str. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_DecodeMBCSStateful(const char *str, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)¶
- Return value: New reference. Part of the Stable ABI on Windows since version 3.7.
If consumed is
NULL
, behave likePyUnicode_DecodeMBCS()
. If consumed is notNULL
,PyUnicode_DecodeMBCSStateful()
will not decode trailing lead byte and the number of bytes that have been decoded will be stored in consumed.
-
PyObject *PyUnicode_DecodeCodePageStateful(int code_page, const char *str, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)¶
- Return value: New reference. Part of the Stable ABI on Windows since version 3.7.
Similar to
PyUnicode_DecodeMBCSStateful()
, except uses the code page specified by code_page.
-
PyObject *PyUnicode_AsMBCSString(PyObject *unicode)¶
- Return value: New reference. Part of the Stable ABI on Windows since version 3.7.
Encode a Unicode object using MBCS and return the result as Python bytes object. Error handling is “strict”. Return
NULL
if an exception was raised by the codec.
-
PyObject *PyUnicode_EncodeCodePage(int code_page, PyObject *unicode, const char *errors)¶
- Return value: New reference. Part of the Stable ABI on Windows since version 3.7.
Encode the Unicode object using the specified code page and return a Python bytes object. Return
NULL
if an exception was raised by the codec. UseCP_ACP
code page to get the MBCS encoder.Added in version 3.3.
Methods and Slot Functions¶
The following APIs are capable of handling Unicode objects and strings on input (we refer to them as strings in the descriptions) and return Unicode objects or integers as appropriate.
They all return NULL
or -1
if an exception occurs.
-
PyObject *PyUnicode_Concat(PyObject *left, PyObject *right)¶
- Return value: New reference. Part of the Stable ABI.
Concat two strings giving a new Unicode string.
-
PyObject *PyUnicode_Split(PyObject *unicode, PyObject *sep, Py_ssize_t maxsplit)¶
- Return value: New reference. Part of the Stable ABI.
Split a string giving a list of Unicode strings. If sep is
NULL
, splitting will be done at all whitespace substrings. Otherwise, splits occur at the given separator. At most maxsplit splits will be done. If negative, no limit is set. Separators are not included in the resulting list.On error, return
NULL
with an exception set.Equivalent to
str.split()
.
-
PyObject *PyUnicode_RSplit(PyObject *unicode, PyObject *sep, Py_ssize_t maxsplit)¶
- Return value: New reference. Part of the Stable ABI.
Similar to
PyUnicode_Split()
, but splitting will be done beginning at the end of the string.On error, return
NULL
with an exception set.Equivalent to
str.rsplit()
.
-
PyObject *PyUnicode_Splitlines(PyObject *unicode, int keepends)¶
- Return value: New reference. Part of the Stable ABI.
Split a Unicode string at line breaks, returning a list of Unicode strings. CRLF is considered to be one line break. If keepends is
0
, the Line break characters are not included in the resulting strings.
-
PyObject *PyUnicode_Partition(PyObject *unicode, PyObject *sep)¶
- Return value: New reference. Part of the Stable ABI.
Split a Unicode string at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing the string itself, followed by two empty strings.
sep must not be empty.
On error, return
NULL
with an exception set.Equivalent to
str.partition()
.
-
PyObject *PyUnicode_RPartition(PyObject *unicode, PyObject *sep)¶
- Return value: New reference. Part of the Stable ABI.
Similar to
PyUnicode_Partition()
, but split a Unicode string at the last occurrence of sep. If the separator is not found, return a 3-tuple containing two empty strings, followed by the string itself.sep must not be empty.
On error, return
NULL
with an exception set.Equivalent to
str.rpartition()
.
-
PyObject *PyUnicode_Join(PyObject *separator, PyObject *seq)¶
- Return value: New reference. Part of the Stable ABI.
Join a sequence of strings using the given separator and return the resulting Unicode string.
-
Py_ssize_t PyUnicode_Tailmatch(PyObject *unicode, PyObject *substr, Py_ssize_t start, Py_ssize_t end, int direction)¶
- Part of the Stable ABI.
Return
1
if substr matchesunicode[start:end]
at the given tail end (direction ==-1
means to do a prefix match, direction ==1
a suffix match),0
otherwise. Return-1
if an error occurred.
-
Py_ssize_t PyUnicode_Find(PyObject *unicode, PyObject *substr, Py_ssize_t start, Py_ssize_t end, int direction)¶
- Part of the Stable ABI.
Return the first position of substr in
unicode[start:end]
using the given direction (direction ==1
means to do a forward search, direction ==-1
a backward search). The return value is the index of the first match; a value of-1
indicates that no match was found, and-2
indicates that an error occurred and an exception has been set.
-
Py_ssize_t PyUnicode_FindChar(PyObject *unicode, Py_UCS4 ch, Py_ssize_t start, Py_ssize_t end, int direction)¶
- Part of the Stable ABI since version 3.7.
Return the first position of the character ch in
unicode[start:end]
using the given direction (direction ==1
means to do a forward search, direction ==-1
a backward search). The return value is the index of the first match; a value of-1
indicates that no match was found, and-2
indicates that an error occurred and an exception has been set.Added in version 3.3.
Changed in version 3.7: start and end are now adjusted to behave like
unicode[start:end]
.
-
Py_ssize_t PyUnicode_Count(PyObject *unicode, PyObject *substr, Py_ssize_t start, Py_ssize_t end)¶
- Part of the Stable ABI.
Return the number of non-overlapping occurrences of substr in
unicode[start:end]
. Return-1
if an error occurred.
-
PyObject *PyUnicode_Replace(PyObject *unicode, PyObject *substr, PyObject *replstr, Py_ssize_t maxcount)¶
- Return value: New reference. Part of the Stable ABI.
Replace at most maxcount occurrences of substr in unicode with replstr and return the resulting Unicode object. maxcount ==
-1
means replace all occurrences.
-
int PyUnicode_Compare(PyObject *left, PyObject *right)¶
- Part of the Stable ABI.
Compare two strings and return
-1
,0
,1
for less than, equal, and greater than, respectively.This function returns
-1
upon failure, so one should callPyErr_Occurred()
to check for errors.See also
The
PyUnicode_Equal()
function.
-
int PyUnicode_Equal(PyObject *a, PyObject *b)¶
- Part of the Stable ABI since version 3.14.
Test if two strings are equal:
Return
1
if a is equal to b.Return
0
if a is not equal to b.Set a
TypeError
exception and return-1
if a or b is not astr
object.
The function always succeeds if a and b are
str
objects.The function works for
str
subclasses, but does not honor custom__eq__()
method.See also
The
PyUnicode_Compare()
function.Added in version 3.14.
-
int PyUnicode_EqualToUTF8AndSize(PyObject *unicode, const char *string, Py_ssize_t size)¶
- Part of the Stable ABI since version 3.13.
Compare a Unicode object with a char buffer which is interpreted as being UTF-8 or ASCII encoded and return true (
1
) if they are equal, or false (0
) otherwise. If the Unicode object contains surrogate code points (U+D800
-U+DFFF
) or the C string is not valid UTF-8, false (0
) is returned.This function does not raise exceptions.
Added in version 3.13.
-
int PyUnicode_EqualToUTF8(PyObject *unicode, const char *string)¶
- Part of the Stable ABI since version 3.13.
Similar to
PyUnicode_EqualToUTF8AndSize()
, but compute string length usingstrlen()
. If the Unicode object contains null characters, false (0
) is returned.Added in version 3.13.
-
int PyUnicode_CompareWithASCIIString(PyObject *unicode, const char *string)¶
- Part of the Stable ABI.
Compare a Unicode object, unicode, with string and return
-1
,0
,1
for less than, equal, and greater than, respectively. It is best to pass only ASCII-encoded strings, but the function interprets the input string as ISO-8859-1 if it contains non-ASCII characters.This function does not raise exceptions.
-
PyObject *PyUnicode_RichCompare(PyObject *left, PyObject *right, int op)¶
- Return value: New reference. Part of the Stable ABI.
Rich compare two Unicode strings and return one of the following:
NULL
in case an exception was raisedPy_NotImplemented
in case the type combination is unknown
Possible values for op are
Py_GT
,Py_GE
,Py_EQ
,Py_NE
,Py_LT
, andPy_LE
.
-
PyObject *PyUnicode_Format(PyObject *format, PyObject *args)¶
- Return value: New reference. Part of the Stable ABI.
Return a new string object from format and args; this is analogous to
format % args
.
-
int PyUnicode_Contains(PyObject *unicode, PyObject *substr)¶
- Part of the Stable ABI.
Check whether substr is contained in unicode and return true or false accordingly.
substr has to coerce to a one element Unicode string.
-1
is returned if there was an error.
-
void PyUnicode_InternInPlace(PyObject **p_unicode)¶
- Part of the Stable ABI.
Intern the argument *p_unicode in place. The argument must be the address of a pointer variable pointing to a Python Unicode string object. If there is an existing interned string that is the same as *p_unicode, it sets *p_unicode to it (releasing the reference to the old string object and creating a new strong reference to the interned string object), otherwise it leaves *p_unicode alone and interns it.
(Clarification: even though there is a lot of talk about references, think of this function as reference-neutral. You must own the object you pass in; after the call you no longer own the passed-in reference, but you newly own the result.)
This function never raises an exception. On error, it leaves its argument unchanged without interning it.
Instances of subclasses of
str
may not be interned, that is, PyUnicode_CheckExact(*p_unicode) must be true. If it is not, then – as with any other error – the argument is left unchanged.Note that interned strings are not “immortal”. You must keep a reference to the result to benefit from interning.
-
PyObject *PyUnicode_InternFromString(const char *str)¶
- Return value: New reference. Part of the Stable ABI.
A combination of
PyUnicode_FromString()
andPyUnicode_InternInPlace()
, meant for statically allocated strings.Return a new (“owned”) reference to either a new Unicode string object that has been interned, or an earlier interned string object with the same value.
Python may keep a reference to the result, or make it immortal, preventing it from being garbage-collected promptly. For interning an unbounded number of different strings, such as ones coming from user input, prefer calling
PyUnicode_FromString()
andPyUnicode_InternInPlace()
directly.
-
unsigned int PyUnicode_CHECK_INTERNED(PyObject *str)¶
Return a non-zero value if str is interned, zero if not. The str argument must be a string; this is not checked. This function always succeeds.
CPython implementation detail: A non-zero return value may carry additional information about how the string is interned. The meaning of such non-zero values, as well as each specific string’s intern-related details, may change between CPython versions.
PyUnicodeWriter¶
The PyUnicodeWriter
API can be used to create a Python str
object.
Added in version 3.14.
-
type PyUnicodeWriter¶
A Unicode writer instance.
The instance must be destroyed by
PyUnicodeWriter_Finish()
on success, orPyUnicodeWriter_Discard()
on error.
-
PyUnicodeWriter *PyUnicodeWriter_Create(Py_ssize_t length)¶
Create a Unicode writer instance.
length must be greater than or equal to
0
.If length is greater than
0
, preallocate an internal buffer of length characters.Set an exception and return
NULL
on error.
-
PyObject *PyUnicodeWriter_Finish(PyUnicodeWriter *writer)¶
Return the final Python
str
object and destroy the writer instance.Set an exception and return
NULL
on error.The writer instance is invalid after this call.
-
void PyUnicodeWriter_Discard(PyUnicodeWriter *writer)¶
Discard the internal Unicode buffer and destroy the writer instance.
If writer is
NULL
, no operation is performed.The writer instance is invalid after this call.
-
int PyUnicodeWriter_WriteChar(PyUnicodeWriter *writer, Py_UCS4 ch)¶
Write the single Unicode character ch into writer.
On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.
-
int PyUnicodeWriter_WriteUTF8(PyUnicodeWriter *writer, const char *str, Py_ssize_t size)¶
Decode the string str from UTF-8 in strict mode and write the output into writer.
size is the string length in bytes. If size is equal to
-1
, callstrlen(str)
to get the string length.On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.See also
PyUnicodeWriter_DecodeUTF8Stateful()
.
-
int PyUnicodeWriter_WriteASCII(PyUnicodeWriter *writer, const char *str, Py_ssize_t size)¶
Write the ASCII string str into writer.
size is the string length in bytes. If size is equal to
-1
, callstrlen(str)
to get the string length.str must only contain ASCII characters. The behavior is undefined if str contains non-ASCII characters.
On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.Added in version 3.14.
-
int PyUnicodeWriter_WriteWideChar(PyUnicodeWriter *writer, const wchar_t *str, Py_ssize_t size)¶
Write the wide string str into writer.
size is a number of wide characters. If size is equal to
-1
, callwcslen(str)
to get the string length.On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.
-
int PyUnicodeWriter_WriteUCS4(PyUnicodeWriter *writer, Py_UCS4 *str, Py_ssize_t size)¶
Writer the UCS4 string str into writer.
size is a number of UCS4 characters.
On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.
-
int PyUnicodeWriter_WriteStr(PyUnicodeWriter *writer, PyObject *obj)¶
Call
PyObject_Str()
on obj and write the output into writer.On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.
-
int PyUnicodeWriter_WriteRepr(PyUnicodeWriter *writer, PyObject *obj)¶
Call
PyObject_Repr()
on obj and write the output into writer.On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.
-
int PyUnicodeWriter_WriteSubstring(PyUnicodeWriter *writer, PyObject *str, Py_ssize_t start, Py_ssize_t end)¶
Write the substring
str[start:end]
into writer.str must be Python
str
object. start must be greater than or equal to 0, and less than or equal to end. end must be less than or equal to str length.On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.
-
int PyUnicodeWriter_Format(PyUnicodeWriter *writer, const char *format, ...)¶
Similar to
PyUnicode_FromFormat()
, but write the output directly into writer.On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.
-
int PyUnicodeWriter_DecodeUTF8Stateful(PyUnicodeWriter *writer, const char *string, Py_ssize_t length, const char *errors, Py_ssize_t *consumed)¶
Decode the string str from UTF-8 with errors error handler and write the output into writer.
size is the string length in bytes. If size is equal to
-1
, callstrlen(str)
to get the string length.errors is an error handler name, such as
"replace"
. If errors isNULL
, use the strict error handler.If consumed is not
NULL
, set *consumed to the number of decoded bytes on success. If consumed isNULL
, treat trailing incomplete UTF-8 byte sequences as an error.On success, return
0
. On error, set an exception, leave the writer unchanged, and return-1
.See also
PyUnicodeWriter_WriteUTF8()
.
Deprecated API¶
The following API is deprecated.
-
type Py_UNICODE¶
This is a typedef of
wchar_t
, which is a 16-bit type or 32-bit type depending on the platform. Please usewchar_t
directly instead.Changed in version 3.3: In previous versions, this was a 16-bit type or a 32-bit type depending on whether you selected a “narrow” or “wide” Unicode version of Python at build time.
Deprecated since version 3.13, will be removed in version 3.15.
-
int PyUnicode_READY(PyObject *unicode)¶
Do nothing and return
0
. This API is kept only for backward compatibility, but there are no plans to remove it.Added in version 3.3.
Deprecated since version 3.10: This API does nothing since Python 3.12. Previously, this needed to be called for each string created using the old API (
PyUnicode_FromUnicode()
or similar).
-
unsigned int PyUnicode_IS_READY(PyObject *unicode)¶
Do nothing and return
1
. This API is kept only for backward compatibility, but there are no plans to remove it.Added in version 3.3.
Deprecated since version 3.14: This API does nothing since Python 3.12. Previously, this could be called to check if
PyUnicode_READY()
is necessary.


3. Defining Extension Types: Assorted Topics¶
This section aims to give a quick fly-by on the various type methods you can implement and what they do.
Here is the definition of PyTypeObject
, with some fields only used in
debug builds omitted:
typedef struct _typeobject {
PyObject_VAR_HEAD
const char *tp_name; /* For printing, in format "<module>.<name>" */
Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */
/* Methods to implement standard operations */
destructor tp_dealloc;
Py_ssize_t tp_vectorcall_offset;
getattrfunc tp_getattr;
setattrfunc tp_setattr;
PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
or tp_reserved (Python 3) */
reprfunc tp_repr;
/* Method suites for standard classes */
PyNumberMethods *tp_as_number;
PySequenceMethods *tp_as_sequence;
PyMappingMethods *tp_as_mapping;
/* More standard operations (here for binary compatibility) */
hashfunc tp_hash;
ternaryfunc tp_call;
reprfunc tp_str;
getattrofunc tp_getattro;
setattrofunc tp_setattro;
/* Functions to access object as input/output buffer */
PyBufferProcs *tp_as_buffer;
/* Flags to define presence of optional/expanded features */
unsigned long tp_flags;
const char *tp_doc; /* Documentation string */
/* Assigned meaning in release 2.0 */
/* call function for all accessible objects */
traverseproc tp_traverse;
/* delete references to contained objects */
inquiry tp_clear;
/* Assigned meaning in release 2.1 */
/* rich comparisons */
richcmpfunc tp_richcompare;
/* weak reference enabler */
Py_ssize_t tp_weaklistoffset;
/* Iterators */
getiterfunc tp_iter;
iternextfunc tp_iternext;
/* Attribute descriptor and subclassing stuff */
PyMethodDef *tp_methods;
PyMemberDef *tp_members;
PyGetSetDef *tp_getset;
// Strong reference on a heap type, borrowed reference on a static type
PyTypeObject *tp_base;
PyObject *tp_dict;
descrgetfunc tp_descr_get;
descrsetfunc tp_descr_set;
Py_ssize_t tp_dictoffset;
initproc tp_init;
allocfunc tp_alloc;
newfunc tp_new;
freefunc tp_free; /* Low-level free-memory routine */
inquiry tp_is_gc; /* For PyObject_IS_GC */
PyObject *tp_bases;
PyObject *tp_mro; /* method resolution order */
PyObject *tp_cache; /* no longer used */
void *tp_subclasses; /* for static builtin types this is an index */
PyObject *tp_weaklist; /* not used for static builtin types */
destructor tp_del;
/* Type attribute cache version tag. Added in version 2.6.
* If zero, the cache is invalid and must be initialized.
*/
unsigned int tp_version_tag;
destructor tp_finalize;
vectorcallfunc tp_vectorcall;
/* bitset of which type-watchers care about this type */
unsigned char tp_watched;
/* Number of tp_version_tag values used.
* Set to _Py_ATTR_CACHE_UNUSED if the attribute cache is
* disabled for this type (e.g. due to custom MRO entries).
* Otherwise, limited to MAX_VERSIONS_PER_CLASS (defined elsewhere).
*/
uint16_t tp_versions_used;
} PyTypeObject;
Now that’s a lot of methods. Don’t worry too much though – if you have a type you want to define, the chances are very good that you will only implement a handful of these.
As you probably expect by now, we’re going to go over this and give more information about the various handlers. We won’t go in the order they are defined in the structure, because there is a lot of historical baggage that impacts the ordering of the fields. It’s often easiest to find an example that includes the fields you need and then change the values to suit your new type.
const char *tp_name; /* For printing */
The name of the type – as mentioned in the previous chapter, this will appear in various places, almost entirely for diagnostic purposes. Try to choose something that will be helpful in such a situation!
Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */
These fields tell the runtime how much memory to allocate when new objects of
this type are created. Python has some built-in support for variable length
structures (think: strings, tuples) which is where the tp_itemsize
field
comes in. This will be dealt with later.
const char *tp_doc;
Here you can put a string (or its address) that you want returned when the
Python script references obj.__doc__
to retrieve the doc string.
Now we come to the basic type methods – the ones most extension types will implement.
3.1. Finalization and De-allocation¶
destructor tp_dealloc;
This function is called when the reference count of the instance of your type is reduced to zero and the Python interpreter wants to reclaim it. If your type has memory to free or other clean-up to perform, you can put it here. The object itself needs to be freed here as well. Here is an example of this function:
static void
newdatatype_dealloc(PyObject *op)
{
newdatatypeobject *self = (newdatatypeobject *) op;
free(self->obj_UnderlyingDatatypePtr);
Py_TYPE(self)->tp_free(self);
}
If your type supports garbage collection, the destructor should call
PyObject_GC_UnTrack()
before clearing any member fields:
static void
newdatatype_dealloc(PyObject *op)
{
newdatatypeobject *self = (newdatatypeobject *) op;
PyObject_GC_UnTrack(op);
Py_CLEAR(self->other_obj);
...
Py_TYPE(self)->tp_free(self);
}
One important requirement of the deallocator function is that it leaves any
pending exceptions alone. This is important since deallocators are frequently
called as the interpreter unwinds the Python stack; when the stack is unwound
due to an exception (rather than normal returns), nothing is done to protect the
deallocators from seeing that an exception has already been set. Any actions
which a deallocator performs which may cause additional Python code to be
executed may detect that an exception has been set. This can lead to misleading
errors from the interpreter. The proper way to protect against this is to save
a pending exception before performing the unsafe action, and restoring it when
done. This can be done using the PyErr_Fetch()
and
PyErr_Restore()
functions:
static void
my_dealloc(PyObject *obj)
{
MyObject *self = (MyObject *) obj;
PyObject *cbresult;
if (self->my_callback != NULL) {
PyObject *err_type, *err_value, *err_traceback;
/* This saves the current exception state */
PyErr_Fetch(&err_type, &err_value, &err_traceback);
cbresult = PyObject_CallNoArgs(self->my_callback);
if (cbresult == NULL) {
PyErr_WriteUnraisable(self->my_callback);
}
else {
Py_DECREF(cbresult);
}
/* This restores the saved exception state */
PyErr_Restore(err_type, err_value, err_traceback);
Py_DECREF(self->my_callback);
}
Py_TYPE(self)->tp_free(self);
}
Note
There are limitations to what you can safely do in a deallocator function.
First, if your type supports garbage collection (using tp_traverse
and/or tp_clear
), some of the object’s members can have been
cleared or finalized by the time tp_dealloc
is called. Second, in
tp_dealloc
, your object is in an unstable state: its reference
count is equal to zero. Any call to a non-trivial object or API (as in the
example above) might end up calling tp_dealloc
again, causing a
double free and a crash.
Starting with Python 3.4, it is recommended not to put any complex
finalization code in tp_dealloc
, and instead use the new
tp_finalize
type method.
See also
PEP 442 explains the new finalization scheme.
3.2. Object Presentation¶
In Python, there are two ways to generate a textual representation of an object:
the repr()
function, and the str()
function. (The print()
function just calls str()
.) These handlers are both optional.
reprfunc tp_repr;
reprfunc tp_str;
The tp_repr
handler should return a string object containing a
representation of the instance for which it is called. Here is a simple
example:
static PyObject *
newdatatype_repr(PyObject *op)
{
newdatatypeobject *self = (newdatatypeobject *) op;
return PyUnicode_FromFormat("Repr-ified_newdatatype{{size:%d}}",
self->obj_UnderlyingDatatypePtr->size);
}
If no tp_repr
handler is specified, the interpreter will supply a
representation that uses the type’s tp_name
and a uniquely identifying
value for the object.
The tp_str
handler is to str()
what the tp_repr
handler
described above is to repr()
; that is, it is called when Python code calls
str()
on an instance of your object. Its implementation is very similar
to the tp_repr
function, but the resulting string is intended for human
consumption. If tp_str
is not specified, the tp_repr
handler is
used instead.
Here is a simple example:
static PyObject *
newdatatype_str(PyObject *op)
{
newdatatypeobject *self = (newdatatypeobject *) op;
return PyUnicode_FromFormat("Stringified_newdatatype{{size:%d}}",
self->obj_UnderlyingDatatypePtr->size);
}
3.3. Attribute Management¶
For every object which can support attributes, the corresponding type must
provide the functions that control how the attributes are resolved. There needs
to be a function which can retrieve attributes (if any are defined), and another
to set attributes (if setting attributes is allowed). Removing an attribute is
a special case, for which the new value passed to the handler is NULL
.
Python supports two pairs of attribute handlers; a type that supports attributes only needs to implement the functions for one pair. The difference is that one pair takes the name of the attribute as a char*, while the other accepts a PyObject*. Each type can use whichever pair makes more sense for the implementation’s convenience.
getattrfunc tp_getattr; /* char * version */
setattrfunc tp_setattr;
/* ... */
getattrofunc tp_getattro; /* PyObject * version */
setattrofunc tp_setattro;
If accessing attributes of an object is always a simple operation (this will be explained shortly), there are generic implementations which can be used to provide the PyObject* version of the attribute management functions. The actual need for type-specific attribute handlers almost completely disappeared starting with Python 2.2, though there are many examples which have not been updated to use some of the new generic mechanism that is available.
3.3.1. Generic Attribute Management¶
Most extension types only use simple attributes. So, what makes the attributes simple? There are only a couple of conditions that must be met:
The name of the attributes must be known when
PyType_Ready()
is called.No special processing is needed to record that an attribute was looked up or set, nor do actions need to be taken based on the value.
Note that this list does not place any restrictions on the values of the attributes, when the values are computed, or how relevant data is stored.
When PyType_Ready()
is called, it uses three tables referenced by the
type object to create descriptors which are placed in the dictionary of the
type object. Each descriptor controls access to one attribute of the instance
object. Each of the tables is optional; if all three are NULL
, instances of
the type will only have attributes that are inherited from their base type, and
should leave the tp_getattro
and tp_setattro
fields NULL
as
well, allowing the base type to handle attributes.
The tables are declared as three fields of the type object:
struct PyMethodDef *tp_methods;
struct PyMemberDef *tp_members;
struct PyGetSetDef *tp_getset;
If tp_methods
is not NULL
, it must refer to an array of
PyMethodDef
structures. Each entry in the table is an instance of this
structure:
typedef struct PyMethodDef {
const char *ml_name; /* method name */
PyCFunction ml_meth; /* implementation function */
int ml_flags; /* flags */
const char *ml_doc; /* docstring */
} PyMethodDef;
One entry should be defined for each method provided by the type; no entries are
needed for methods inherited from a base type. One additional entry is needed
at the end; it is a sentinel that marks the end of the array. The
ml_name
field of the sentinel must be NULL
.
The second table is used to define attributes which map directly to data stored in the instance. A variety of primitive C types are supported, and access may be read-only or read-write. The structures in the table are defined as:
typedef struct PyMemberDef {
const char *name;
int type;
int offset;
int flags;
const char *doc;
} PyMemberDef;
For each entry in the table, a descriptor will be constructed and added to the
type which will be able to extract a value from the instance structure. The
type
field should contain a type code like Py_T_INT
or
Py_T_DOUBLE
; the value will be used to determine how to
convert Python values to and from C values. The flags
field is used to
store flags which control how the attribute can be accessed: you can set it to
Py_READONLY
to prevent Python code from setting it.
An interesting advantage of using the tp_members
table to build
descriptors that are used at runtime is that any attribute defined this way can
have an associated doc string simply by providing the text in the table. An
application can use the introspection API to retrieve the descriptor from the
class object, and get the doc string using its __doc__
attribute.
As with the tp_methods
table, a sentinel entry with a ml_name
value
of NULL
is required.
3.3.2. Type-specific Attribute Management¶
For simplicity, only the char* version will be demonstrated here; the type of the name parameter is the only difference between the char* and PyObject* flavors of the interface. This example effectively does the same thing as the generic example above, but does not use the generic support added in Python 2.2. It explains how the handler functions are called, so that if you do need to extend their functionality, you’ll understand what needs to be done.
The tp_getattr
handler is called when the object requires an attribute
look-up. It is called in the same situations where the __getattr__()
method of a class would be called.
Here is an example:
static PyObject *
newdatatype_getattr(PyObject *op, char *name)
{
newdatatypeobject *self = (newdatatypeobject *) op;
if (strcmp(name, "data") == 0) {
return PyLong_FromLong(self->data);
}
PyErr_Format(PyExc_AttributeError,
"'%.100s' object has no attribute '%.400s'",
Py_TYPE(self)->tp_name, name);
return NULL;
}
The tp_setattr
handler is called when the __setattr__()
or
__delattr__()
method of a class instance would be called. When an
attribute should be deleted, the third parameter will be NULL
. Here is an
example that simply raises an exception; if this were really all you wanted, the
tp_setattr
handler should be set to NULL
.
static int
newdatatype_setattr(PyObject *op, char *name, PyObject *v)
{
PyErr_Format(PyExc_RuntimeError, "Read-only attribute: %s", name);
return -1;
}
3.4. Object Comparison¶
richcmpfunc tp_richcompare;
The tp_richcompare
handler is called when comparisons are needed. It is
analogous to the rich comparison methods, like
__lt__()
, and also called by PyObject_RichCompare()
and
PyObject_RichCompareBool()
.
This function is called with two Python objects and the operator as arguments,
where the operator is one of Py_EQ
, Py_NE
, Py_LE
, Py_GE
,
Py_LT
or Py_GT
. It should compare the two objects with respect to the
specified operator and return Py_True
or Py_False
if the comparison is
successful, Py_NotImplemented
to indicate that comparison is not
implemented and the other object’s comparison method should be tried, or NULL
if an exception was set.
Here is a sample implementation, for a datatype that is considered equal if the size of an internal pointer is equal:
static PyObject *
newdatatype_richcmp(PyObject *lhs, PyObject *rhs, int op)
{
newdatatypeobject *obj1 = (newdatatypeobject *) lhs;
newdatatypeobject *obj2 = (newdatatypeobject *) rhs;
PyObject *result;
int c, size1, size2;
/* code to make sure that both arguments are of type
newdatatype omitted */
size1 = obj1->obj_UnderlyingDatatypePtr->size;
size2 = obj2->obj_UnderlyingDatatypePtr->size;
switch (op) {
case Py_LT: c = size1 < size2; break;
case Py_LE: c = size1 <= size2; break;
case Py_EQ: c = size1 == size2; break;
case Py_NE: c = size1 != size2; break;
case Py_GT: c = size1 > size2; break;
case Py_GE: c = size1 >= size2; break;
}
result = c ? Py_True : Py_False;
return Py_NewRef(result);
}
3.5. Abstract Protocol Support¶
Python supports a variety of abstract ‘protocols;’ the specific interfaces provided to use these interfaces are documented in Abstract Objects Layer.
A number of these abstract interfaces were defined early in the development of
the Python implementation. In particular, the number, mapping, and sequence
protocols have been part of Python since the beginning. Other protocols have
been added over time. For protocols which depend on several handler routines
from the type implementation, the older protocols have been defined as optional
blocks of handlers referenced by the type object. For newer protocols there are
additional slots in the main type object, with a flag bit being set to indicate
that the slots are present and should be checked by the interpreter. (The flag
bit does not indicate that the slot values are non-NULL
. The flag may be set
to indicate the presence of a slot, but a slot may still be unfilled.)
PyNumberMethods *tp_as_number;
PySequenceMethods *tp_as_sequence;
PyMappingMethods *tp_as_mapping;
If you wish your object to be able to act like a number, a sequence, or a
mapping object, then you place the address of a structure that implements the C
type PyNumberMethods
, PySequenceMethods
, or
PyMappingMethods
, respectively. It is up to you to fill in this
structure with appropriate values. You can find examples of the use of each of
these in the Objects
directory of the Python source distribution.
hashfunc tp_hash;
This function, if you choose to provide it, should return a hash number for an instance of your data type. Here is a simple example:
static Py_hash_t
newdatatype_hash(PyObject *op)
{
newdatatypeobject *self = (newdatatypeobject *) op;
Py_hash_t result;
result = self->some_size + 32767 * self->some_number;
if (result == -1) {
result = -2;
}
return result;
}
Py_hash_t
is a signed integer type with a platform-varying width.
Returning -1
from tp_hash
indicates an error,
which is why you should be careful to avoid returning it when hash computation
is successful, as seen above.
ternaryfunc tp_call;
This function is called when an instance of your data type is “called”, for
example, if obj1
is an instance of your data type and the Python script
contains obj1('hello')
, the tp_call
handler is invoked.
This function takes three arguments:
self is the instance of the data type which is the subject of the call. If the call is
obj1('hello')
, then self isobj1
.args is a tuple containing the arguments to the call. You can use
PyArg_ParseTuple()
to extract the arguments.kwds is a dictionary of keyword arguments that were passed. If this is non-
NULL
and you support keyword arguments, usePyArg_ParseTupleAndKeywords()
to extract the arguments. If you do not want to support keyword arguments and this is non-NULL
, raise aTypeError
with a message saying that keyword arguments are not supported.
Here is a toy tp_call
implementation:
static PyObject *
newdatatype_call(PyObject *op, PyObject *args, PyObject *kwds)
{
newdatatypeobject *self = (newdatatypeobject *) op;
PyObject *result;
const char *arg1;
const char *arg2;
const char *arg3;
if (!PyArg_ParseTuple(args, "sss:call", &arg1, &arg2, &arg3)) {
return NULL;
}
result = PyUnicode_FromFormat(
"Returning -- value: [%d] arg1: [%s] arg2: [%s] arg3: [%s]\n",
self->obj_UnderlyingDatatypePtr->size,
arg1, arg2, arg3);
return result;
}
/* Iterators */
getiterfunc tp_iter;
iternextfunc tp_iternext;
These functions provide support for the iterator protocol. Both handlers
take exactly one parameter, the instance for which they are being called,
and return a new reference. In the case of an error, they should set an
exception and return NULL
. tp_iter
corresponds
to the Python __iter__()
method, while tp_iternext
corresponds to the Python __next__()
method.
Any iterable object must implement the tp_iter
handler, which must return an iterator object. Here the same guidelines
apply as for Python classes:
For collections (such as lists and tuples) which can support multiple independent iterators, a new iterator should be created and returned by each call to
tp_iter
.Objects which can only be iterated over once (usually due to side effects of iteration, such as file objects) can implement
tp_iter
by returning a new reference to themselves – and should also therefore implement thetp_iternext
handler.
Any iterator object should implement both tp_iter
and tp_iternext
. An iterator’s
tp_iter
handler should return a new reference
to the iterator. Its tp_iternext
handler should
return a new reference to the next object in the iteration, if there is one.
If the iteration has reached the end, tp_iternext
may return NULL
without setting an exception, or it may set
StopIteration
in addition to returning NULL
; avoiding
the exception can yield slightly better performance. If an actual error
occurs, tp_iternext
should always set an exception
and return NULL
.
3.6. Weak Reference Support¶
One of the goals of Python’s weak reference implementation is to allow any type to participate in the weak reference mechanism without incurring the overhead on performance-critical objects (such as numbers).
See also
Documentation for the weakref
module.
For an object to be weakly referenceable, the extension type must set the
Py_TPFLAGS_MANAGED_WEAKREF
bit of the tp_flags
field. The legacy tp_weaklistoffset
field should
be left as zero.
Concretely, here is how the statically declared type object would look:
static PyTypeObject TrivialType = {
PyVarObject_HEAD_INIT(NULL, 0)
/* ... other members omitted for brevity ... */
.tp_flags = Py_TPFLAGS_MANAGED_WEAKREF | ...,
};
The only further addition is that tp_dealloc
needs to clear any weak
references (by calling PyObject_ClearWeakRefs()
):
static void
Trivial_dealloc(PyObject *op)
{
/* Clear weakrefs first before calling any destructors */
PyObject_ClearWeakRefs(op);
/* ... remainder of destruction code omitted for brevity ... */
Py_TYPE(op)->tp_free(op);
}
3.7. More Suggestions¶
In order to learn how to implement any specific method for your new data type,
get the CPython source code. Go to the Objects
directory,
then search the C source files for tp_
plus the function you want
(for example, tp_richcompare
). You will find examples of the function
you want to implement.
When you need to verify that an object is a concrete instance of the type you
are implementing, use the PyObject_TypeCheck()
function. A sample of
its use might be something like the following:
if (!PyObject_TypeCheck(some_object, &MyType)) {
PyErr_SetString(PyExc_TypeError, "arg #1 not a mything");
return NULL;
}
See also
- Download CPython source releases.
- The CPython project on GitHub, where the CPython source code is developed.


: Exception and Defect classes

email.errors
: Exception and Defect classes¶
Source code: Lib/email/errors.py
The following exception classes are defined in the email.errors
module:
- exception email.errors.MessageError¶
This is the base class for all exceptions that the
email
package can raise. It is derived from the standardException
class and defines no additional methods.
- exception email.errors.MessageParseError¶
This is the base class for exceptions raised by the
Parser
class. It is derived fromMessageError
. This class is also used internally by the parser used byheaderregistry
.
- exception email.errors.HeaderParseError¶
Raised under some error conditions when parsing the RFC 5322 headers of a message, this class is derived from
MessageParseError
. Theset_boundary()
method will raise this error if the content type is unknown when the method is called.Header
may raise this error for certain base64 decoding errors, and when an attempt is made to create a header that appears to contain an embedded header (that is, there is what is supposed to be a continuation line that has no leading whitespace and looks like a header).
- exception email.errors.BoundaryError¶
Deprecated and no longer used.
- exception email.errors.MultipartConversionError¶
Raised if the
attach()
method is called on an instance of a class derived fromMIMENonMultipart
(e.g.MIMEImage
).MultipartConversionError
multiply inherits fromMessageError
and the built-inTypeError
.
- exception email.errors.HeaderWriteError¶
Raised when an error occurs when the
generator
outputs headers.
- exception email.errors.MessageDefect¶
This is the base class for all defects found when parsing email messages. It is derived from
ValueError
.
- exception email.errors.HeaderDefect¶
This is the base class for all defects found when parsing email headers. It is derived from
MessageDefect
.
Here is the list of the defects that the FeedParser
can find while parsing messages. Note that the defects are added to the message
where the problem was found, so for example, if a message nested inside a
multipart/alternative had a malformed header, that nested message
object would have a defect, but the containing messages would not.
All defect classes are subclassed from email.errors.MessageDefect
.
- exception email.errors.NoBoundaryInMultipartDefect¶
A message claimed to be a multipart, but had no boundary parameter.
- exception email.errors.StartBoundaryNotFoundDefect¶
The start boundary claimed in the Content-Type header was never found.
- exception email.errors.CloseBoundaryNotFoundDefect¶
A start boundary was found, but no corresponding close boundary was ever found.
Added in version 3.3.
- exception email.errors.FirstHeaderLineIsContinuationDefect¶
The message had a continuation line as its first header line.
- exception email.errors.MisplacedEnvelopeHeaderDefect¶
A “Unix From” header was found in the middle of a header block.
- exception email.errors.MissingHeaderBodySeparatorDefect¶
A line was found while parsing headers that had no leading white space but contained no ‘:’. Parsing continues assuming that the line represents the first line of the body.
Added in version 3.3.
- exception email.errors.MalformedHeaderDefect¶
A header was found that was missing a colon, or was otherwise malformed.
Deprecated since version 3.3: This defect has not been used for several Python versions.
- exception email.errors.MultipartInvariantViolationDefect¶
A message claimed to be a multipart, but no subparts were found. Note that when a message has this defect, its
is_multipart()
method may returnFalse
even though its content type claims to be multipart.
- exception email.errors.InvalidBase64PaddingDefect¶
When decoding a block of base64 encoded bytes, the padding was not correct. Enough padding is added to perform the decode, but the resulting decoded bytes may be invalid.
- exception email.errors.InvalidBase64CharactersDefect¶
When decoding a block of base64 encoded bytes, characters outside the base64 alphabet were encountered. The characters are ignored, but the resulting decoded bytes may be invalid.
- exception email.errors.InvalidBase64LengthDefect¶
When decoding a block of base64 encoded bytes, the number of non-padding base64 characters was invalid (1 more than a multiple of 4). The encoded block was kept as-is.
- exception email.errors.InvalidDateDefect¶
When decoding an invalid or unparsable date field. The original value is kept as-is.


Top-level components

9. Top-level components¶
The Python interpreter can get its input from a number of sources: from a script passed to it as standard input or as program argument, typed in interactively, from a module source file, etc. This chapter gives the syntax used in these cases.
9.1. Complete Python programs¶
While a language specification need not prescribe how the language interpreter
is invoked, it is useful to have a notion of a complete Python program. A
complete Python program is executed in a minimally initialized environment: all
built-in and standard modules are available, but none have been initialized,
except for sys
(various system services), builtins
(built-in
functions, exceptions and None
) and __main__
. The latter is used to
provide the local and global namespace for execution of the complete program.
The syntax for a complete Python program is that for file input, described in the next section.
The interpreter may also be invoked in interactive mode; in this case, it does
not read and execute a complete program but reads and executes one statement
(possibly compound) at a time. The initial environment is identical to that of
a complete program; each statement is executed in the namespace of
__main__
.
A complete program can be passed to the interpreter
in three forms: with the -c
string command line option, as a file
passed as the first command line argument, or as standard input. If the file
or standard input is a tty device, the interpreter enters interactive mode;
otherwise, it executes the file as a complete program.
9.2. File input¶
All input read from non-interactive files has the same form:
file_input: (NEWLINE | statement
)* ENDMARKER
This syntax is used in the following situations:
when parsing a complete Python program (from a file or from a string);
when parsing a module;
when parsing a string passed to the
exec()
function;
9.3. Interactive input¶
Input in interactive mode is parsed using the following grammar:
interactive_input: [stmt_list
] NEWLINE |compound_stmt
NEWLINE | ENDMARKER
Note that a (top-level) compound statement must be followed by a blank line in interactive mode; this is needed to help the parser detect the end of the input.
9.4. Expression input¶
eval()
is used for expression input. It ignores leading whitespace. The
string argument to eval()
must have the following form:
eval_input: expression_list
NEWLINE* ENDMARKER


Migrating

Migrating optparse
code to argparse
¶
The argparse
module offers several higher level features not natively
provided by the optparse
module, including:
Handling positional arguments.
Supporting subcommands.
Allowing alternative option prefixes like
+
and/
.Handling zero-or-more and one-or-more style arguments.
Producing more informative usage messages.
Providing a much simpler interface for custom
type
andaction
.
Originally, the argparse
module attempted to maintain compatibility
with optparse
. However, the fundamental design differences between
supporting declarative command line option processing (while leaving positional
argument processing to application code), and supporting both named options
and positional arguments in the declarative interface mean that the
API has diverged from that of optparse
over time.
As described in Choosing an argument parsing library, applications that are
currently using optparse
and are happy with the way it works can
just continue to use optparse
.
Application developers that are considering migrating should also review the list of intrinsic behavioural differences described in that section before deciding whether or not migration is desirable.
For applications that do choose to migrate from optparse
to argparse
,
the following suggestions should be helpful:
Replace all
optparse.OptionParser.add_option()
calls withArgumentParser.add_argument()
calls.Replace
(options, args) = parser.parse_args()
withargs = parser.parse_args()
and add additionalArgumentParser.add_argument()
calls for the positional arguments. Keep in mind that what was previously calledoptions
, now in theargparse
context is calledargs
.Replace
optparse.OptionParser.disable_interspersed_args()
by usingparse_intermixed_args()
instead ofparse_args()
.Replace callback actions and the
callback_*
keyword arguments withtype
oraction
arguments.Replace string names for
type
keyword arguments with the corresponding type objects (e.g. int, float, complex, etc).Replace
optparse.Values
withNamespace
andoptparse.OptionError
andoptparse.OptionValueError
withArgumentError
.Replace strings with implicit arguments such as
%default
or%prog
with the standard Python syntax to use dictionaries to format strings, that is,%(default)s
and%(prog)s
.Replace the OptionParser constructor
version
argument with a call toparser.add_argument('--version', action='version', version='<the version>')
.