What’s New In Python 3.3

What’s New In Python 3.3¶
This article explains the new features in Python 3.3, compared to 3.2. Python 3.3 was released on September 29, 2012. For full details, see the changelog.
See also
PEP 398 - Python 3.3 Release Schedule
Summary – Release highlights¶
New syntax features:
New
yield from
expression for generator delegation.The
u'unicode'
syntax is accepted again forstr
objects.
New library modules:
faulthandler
(helps debugging low-level crashes)ipaddress
(high-level objects representing IP addresses and masks)lzma
(compress data using the XZ / LZMA algorithm)unittest.mock
(replace parts of your system under test with mock objects)venv
(Python virtual environments, as in the popularvirtualenv
package)
New built-in features:
Reworked I/O exception hierarchy.
Implementation improvements:
Rewritten import machinery based on
importlib
.More compact unicode strings.
More compact attribute dictionaries.
Significantly Improved Library Modules:
C Accelerator for the decimal module.
Better unicode handling in the email module (provisional).
Security improvements:
Hash randomization is switched on by default.
Please read on for a comprehensive list of user-facing changes.
PEP 405: Virtual Environments¶
Virtual environments help create separate Python setups while sharing a
system-wide base install, for ease of maintenance. Virtual environments
have their own set of private site packages (i.e. locally installed
libraries), and are optionally segregated from the system-wide site
packages. Their concept and implementation are inspired by the popular
virtualenv
third-party package, but benefit from tighter integration
with the interpreter core.
This PEP adds the venv
module for programmatic access, and the
pyvenv
script for command-line access and
administration. The Python interpreter checks for a pyvenv.cfg
,
file whose existence signals the base of a virtual environment’s directory
tree.
See also
- PEP 405 - Python Virtual Environments
PEP written by Carl Meyer; implementation by Carl Meyer and Vinay Sajip
PEP 420: Implicit Namespace Packages¶
Native support for package directories that don’t require __init__.py
marker files and can automatically span multiple path segments (inspired by
various third party approaches to namespace packages, as described in
PEP 420)
See also
- PEP 420 - Implicit Namespace Packages
PEP written by Eric V. Smith; implementation by Eric V. Smith and Barry Warsaw
PEP 3118: New memoryview implementation and buffer protocol documentation¶
The implementation of PEP 3118 has been significantly improved.
The new memoryview implementation comprehensively fixes all ownership and lifetime issues of dynamically allocated fields in the Py_buffer struct that led to multiple crash reports. Additionally, several functions that crashed or returned incorrect results for non-contiguous or multi-dimensional input have been fixed.
The memoryview object now has a PEP-3118 compliant getbufferproc() that checks the consumer’s request type. Many new features have been added, most of them work in full generality for non-contiguous arrays and arrays with suboffsets.
The documentation has been updated, clearly spelling out responsibilities for both exporters and consumers. Buffer request flags are grouped into basic and compound flags. The memory layout of non-contiguous and multi-dimensional NumPy-style arrays is explained.
Features¶
All native single character format specifiers in struct module syntax (optionally prefixed with ‘@’) are now supported.
With some restrictions, the cast() method allows changing of format and shape of C-contiguous arrays.
Multi-dimensional list representations are supported for any array type.
Multi-dimensional comparisons are supported for any array type.
One-dimensional memoryviews of hashable (read-only) types with formats B, b or c are now hashable. (Contributed by Antoine Pitrou in bpo-13411.)
Arbitrary slicing of any 1-D arrays type is supported. For example, it is now possible to reverse a memoryview in O(1) by using a negative step.
API changes¶
The maximum number of dimensions is officially limited to 64.
The representation of empty shape, strides and suboffsets is now an empty tuple instead of
None
.Accessing a memoryview element with format ‘B’ (unsigned bytes) now returns an integer (in accordance with the struct module syntax). For returning a bytes object the view must be cast to ‘c’ first.
memoryview comparisons now use the logical structure of the operands and compare all array elements by value. All format strings in struct module syntax are supported. Views with unrecognised format strings are still permitted, but will always compare as unequal, regardless of view contents.
For further changes see Build and C API Changes and Porting C code.
(Contributed by Stefan Krah in bpo-10181.)
See also
PEP 3118 - Revising the Buffer Protocol
PEP 393: Flexible String Representation¶
The Unicode string type is changed to support multiple internal representations, depending on the character with the largest Unicode ordinal (1, 2, or 4 bytes) in the represented string. This allows a space-efficient representation in common cases, but gives access to full UCS-4 on all systems. For compatibility with existing APIs, several representations may exist in parallel; over time, this compatibility should be phased out.
On the Python side, there should be no downside to this change.
On the C API side, PEP 393 is fully backward compatible. The legacy API should remain available at least five years. Applications using the legacy API will not fully benefit of the memory reduction, or - worse - may use a bit more memory, because Python may have to maintain two versions of each string (in the legacy format and in the new efficient storage).
Functionality¶
Changes introduced by PEP 393 are the following:
Python now always supports the full range of Unicode code points, including non-BMP ones (i.e. from
U+0000
toU+10FFFF
). The distinction between narrow and wide builds no longer exists and Python now behaves like a wide build, even under Windows.With the death of narrow builds, the problems specific to narrow builds have also been fixed, for example:
len()
now always returns 1 for non-BMP characters, solen('\U0010FFFF') == 1
;surrogate pairs are not recombined in string literals, so
'\uDBFF\uDFFF' != '\U0010FFFF'
;indexing or slicing non-BMP characters returns the expected value, so
'\U0010FFFF'[0]
now returns'\U0010FFFF'
and not'\uDBFF'
;all other functions in the standard library now correctly handle non-BMP code points.
The value of
sys.maxunicode
is now always1114111
(0x10FFFF
in hexadecimal). ThePyUnicode_GetMax()
function still returns either0xFFFF
or0x10FFFF
for backward compatibility, and it should not be used with the new Unicode API (see bpo-13054).The
./configure
flag--with-wide-unicode
has been removed.
Performance and resource usage¶
The storage of Unicode strings now depends on the highest code point in the string:
pure ASCII and Latin1 strings (
U+0000-U+00FF
) use 1 byte per code point;BMP strings (
U+0000-U+FFFF
) use 2 bytes per code point;non-BMP strings (
U+10000-U+10FFFF
) use 4 bytes per code point.
The net effect is that for most applications, memory usage of string storage should decrease significantly - especially compared to former wide unicode builds - as, in many cases, strings will be pure ASCII even in international contexts (because many strings store non-human language data, such as XML fragments, HTTP headers, JSON-encoded data, etc.). We also hope that it will, for the same reasons, increase CPU cache efficiency on non-trivial applications. The memory usage of Python 3.3 is two to three times smaller than Python 3.2, and a little bit better than Python 2.7, on a Django benchmark (see the PEP for details).
See also
- PEP 393 - Flexible String Representation
PEP written by Martin von Löwis; implementation by Torsten Becker and Martin von Löwis.
PEP 397: Python Launcher for Windows¶
The Python 3.3 Windows installer now includes a py
launcher application
that can be used to launch Python applications in a version independent
fashion.
This launcher is invoked implicitly when double-clicking *.py
files.
If only a single Python version is installed on the system, that version
will be used to run the file. If multiple versions are installed, the most
recent version is used by default, but this can be overridden by including
a Unix-style “shebang line” in the Python script.
The launcher can also be used explicitly from the command line as the py
application. Running py
follows the same version selection rules as
implicitly launching scripts, but a more specific version can be selected
by passing appropriate arguments (such as -3
to request Python 3 when
Python 2 is also installed, or -2.6
to specifically request an earlier
Python version when a more recent version is installed).
In addition to the launcher, the Windows installer now includes an option to add the newly installed Python to the system PATH. (Contributed by Brian Curtin in bpo-3561.)
See also
- PEP 397 - Python Launcher for Windows
PEP written by Mark Hammond and Martin v. Löwis; implementation by Vinay Sajip.
Launcher documentation: Python install manager
Installer PATH modification: Python install manager
PEP 3151: Reworking the OS and IO exception hierarchy¶
The hierarchy of exceptions raised by operating system errors is now both simplified and finer-grained.
You don’t have to worry anymore about choosing the appropriate exception
type between OSError
, IOError
, EnvironmentError
,
WindowsError
, mmap.error
, socket.error
or
select.error
. All these exception types are now only one:
OSError
. The other names are kept as aliases for compatibility
reasons.
Also, it is now easier to catch a specific error condition. Instead of
inspecting the errno
attribute (or args[0]
) for a particular
constant from the errno
module, you can catch the adequate
OSError
subclass. The available subclasses are the following:
And the ConnectionError
itself has finer-grained subclasses:
Thanks to the new exceptions, common usages of the errno
can now be
avoided. For example, the following code written for Python 3.2:
from errno import ENOENT, EACCES, EPERM
try:
with open("document.txt") as f:
content = f.read()
except IOError as err:
if err.errno == ENOENT:
print("document.txt file is missing")
elif err.errno in (EACCES, EPERM):
print("You are not allowed to read document.txt")
else:
raise
can now be written without the errno
import and without manual
inspection of exception attributes:
try:
with open("document.txt") as f:
content = f.read()
except FileNotFoundError:
print("document.txt file is missing")
except PermissionError:
print("You are not allowed to read document.txt")
See also
- PEP 3151 - Reworking the OS and IO Exception Hierarchy
PEP written and implemented by Antoine Pitrou
PEP 380: Syntax for Delegating to a Subgenerator¶
PEP 380 adds the yield from
expression, allowing a generator to
delegate
part of its operations to another generator. This allows a section of code
containing yield
to be factored out and placed in another generator.
Additionally, the subgenerator is allowed to return with a value, and the
value is made available to the delegating generator.
While designed primarily for use in delegating to a subgenerator, the yield
from
expression actually allows delegation to arbitrary subiterators.
For simple iterators, yield from iterable
is essentially just a shortened
form of for item in iterable: yield item
:
>>> def g(x):
... yield from range(x, 0, -1)
... yield from range(x)
...
>>> list(g(5))
[5, 4, 3, 2, 1, 0, 1, 2, 3, 4]
However, unlike an ordinary loop, yield from
allows subgenerators to
receive sent and thrown values directly from the calling scope, and
return a final value to the outer generator:
>>> def accumulate():
... tally = 0
... while 1:
... next = yield
... if next is None:
... return tally
... tally += next
...
>>> def gather_tallies(tallies):
... while 1:
... tally = yield from accumulate()
... tallies.append(tally)
...
>>> tallies = []
>>> acc = gather_tallies(tallies)
>>> next(acc) # Ensure the accumulator is ready to accept values
>>> for i in range(4):
... acc.send(i)
...
>>> acc.send(None) # Finish the first tally
>>> for i in range(5):
... acc.send(i)
...
>>> acc.send(None) # Finish the second tally
>>> tallies
[6, 10]
The main principle driving this change is to allow even generators that are
designed to be used with the send
and throw
methods to be split into
multiple subgenerators as easily as a single large function can be split into
multiple subfunctions.
See also
- PEP 380 - Syntax for Delegating to a Subgenerator
PEP written by Greg Ewing; implementation by Greg Ewing, integrated into 3.3 by Renaud Blanch, Ryan Kelly and Nick Coghlan; documentation by Zbigniew Jędrzejewski-Szmek and Nick Coghlan
PEP 409: Suppressing exception context¶
PEP 409 introduces new syntax that allows the display of the chained exception context to be disabled. This allows cleaner error messages in applications that convert between exception types:
>>> class D:
... def __init__(self, extra):
... self._extra_attributes = extra
... def __getattr__(self, attr):
... try:
... return self._extra_attributes[attr]
... except KeyError:
... raise AttributeError(attr) from None
...
>>> D({}).x
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 8, in __getattr__
AttributeError: x
Without the from None
suffix to suppress the cause, the original
exception would be displayed by default:
>>> class C:
... def __init__(self, extra):
... self._extra_attributes = extra
... def __getattr__(self, attr):
... try:
... return self._extra_attributes[attr]
... except KeyError:
... raise AttributeError(attr)
...
>>> C({}).x
Traceback (most recent call last):
File "<stdin>", line 6, in __getattr__
KeyError: 'x'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 8, in __getattr__
AttributeError: x
No debugging capability is lost, as the original exception context remains available if needed (for example, if an intervening library has incorrectly suppressed valuable underlying details):
>>> try:
... D({}).x
... except AttributeError as exc:
... print(repr(exc.__context__))
...
KeyError('x',)
See also
- PEP 409 - Suppressing exception context
PEP written by Ethan Furman; implemented by Ethan Furman and Nick Coghlan.
PEP 414: Explicit Unicode literals¶
To ease the transition from Python 2 for Unicode aware Python applications
that make heavy use of Unicode literals, Python 3.3 once again supports the
“u
” prefix for string literals. This prefix has no semantic significance
in Python 3, it is provided solely to reduce the number of purely mechanical
changes in migrating to Python 3, making it easier for developers to focus on
the more significant semantic changes (such as the stricter default
separation of binary and text data).
See also
- PEP 414 - Explicit Unicode literals
PEP written by Armin Ronacher.
PEP 3155: Qualified name for classes and functions¶
Functions and class objects have a new __qualname__
attribute representing
the “path” from the module top-level to their definition. For global functions
and classes, this is the same as __name__
.
For other functions and classes,
it provides better information about where they were actually defined, and
how they might be accessible from the global scope.
Example with (non-bound) methods:
>>> class C:
... def meth(self):
... pass
...
>>> C.meth.__name__
'meth'
>>> C.meth.__qualname__
'C.meth'
Example with nested classes:
>>> class C:
... class D:
... def meth(self):
... pass
...
>>> C.D.__name__
'D'
>>> C.D.__qualname__
'C.D'
>>> C.D.meth.__name__
'meth'
>>> C.D.meth.__qualname__
'C.D.meth'
Example with nested functions:
>>> def outer():
... def inner():
... pass
... return inner
...
>>> outer().__name__
'inner'
>>> outer().__qualname__
'outer.<locals>.inner'
The string representation of those objects is also changed to include the new, more precise information:
>>> str(C.D)
"<class '__main__.C.D'>"
>>> str(C.D.meth)
'<function C.D.meth at 0x7f46b9fe31e0>'
See also
- PEP 3155 - Qualified name for classes and functions
PEP written and implemented by Antoine Pitrou.
PEP 412: Key-Sharing Dictionary¶
Dictionaries used for the storage of objects’ attributes are now able to share part of their internal storage between each other (namely, the part which stores the keys and their respective hashes). This reduces the memory consumption of programs creating many instances of non-builtin types.
See also
- PEP 412 - Key-Sharing Dictionary
PEP written and implemented by Mark Shannon.
PEP 362: Function Signature Object¶
A new function inspect.signature()
makes introspection of python
callables easy and straightforward. A broad range of callables is supported:
python functions, decorated or not, classes, and functools.partial()
objects. New classes inspect.Signature
, inspect.Parameter
and inspect.BoundArguments
hold information about the call signatures,
such as, annotations, default values, parameters kinds, and bound arguments,
which considerably simplifies writing decorators and any code that validates
or amends calling signatures or arguments.
See also
- PEP 362: - Function Signature Object
PEP written by Brett Cannon, Yury Selivanov, Larry Hastings, Jiwon Seo; implemented by Yury Selivanov.
PEP 421: Adding sys.implementation¶
A new attribute on the sys
module exposes details specific to the
implementation of the currently running interpreter. The initial set of
attributes on sys.implementation
are name
, version
,
hexversion
, and cache_tag
.
The intention of sys.implementation
is to consolidate into one namespace
the implementation-specific data used by the standard library. This allows
different Python implementations to share a single standard library code base
much more easily. In its initial state, sys.implementation
holds only a
small portion of the implementation-specific data. Over time that ratio will
shift in order to make the standard library more portable.
One example of improved standard library portability is cache_tag
. As of
Python 3.3, sys.implementation.cache_tag
is used by importlib
to
support PEP 3147 compliance. Any Python implementation that uses
importlib
for its built-in import system may use cache_tag
to control
the caching behavior for modules.
SimpleNamespace¶
The implementation of sys.implementation
also introduces a new type to
Python: types.SimpleNamespace
. In contrast to a mapping-based
namespace, like dict
, SimpleNamespace
is attribute-based, like
object
. However, unlike object
, SimpleNamespace
instances
are writable. This means that you can add, remove, and modify the namespace
through normal attribute access.
See also
- PEP 421 - Adding sys.implementation
PEP written and implemented by Eric Snow.
Using importlib as the Implementation of Import¶
bpo-2377 - Replace __import__ w/ importlib.__import__
bpo-13959 - Re-implement parts of imp
in pure Python
bpo-14605 - Make import machinery explicit
bpo-14646 - Require loaders set __loader__ and __package__
The __import__()
function is now powered by importlib.__import__()
.
This work leads to the completion of “phase 2” of PEP 302. There are
multiple benefits to this change. First, it has allowed for more of the
machinery powering import to be exposed instead of being implicit and hidden
within the C code. It also provides a single implementation for all Python VMs
supporting Python 3.3 to use, helping to end any VM-specific deviations in
import semantics. And finally it eases the maintenance of import, allowing for
future growth to occur.
For the common user, there should be no visible change in semantics. For those whose code currently manipulates import or calls import programmatically, the code changes that might possibly be required are covered in the Porting Python code section of this document.
New APIs¶
One of the large benefits of this work is the exposure of what goes into
making the import statement work. That means the various importers that were
once implicit are now fully exposed as part of the importlib
package.
The abstract base classes defined in importlib.abc
have been expanded
to properly delineate between meta path finders
and path entry finders by introducing
importlib.abc.MetaPathFinder
and
importlib.abc.PathEntryFinder
, respectively. The old ABC of
importlib.abc.Finder
is now only provided for backwards-compatibility
and does not enforce any method requirements.
In terms of finders, importlib.machinery.FileFinder
exposes the
mechanism used to search for source and bytecode files of a module. Previously
this class was an implicit member of sys.path_hooks
.
For loaders, the new abstract base class importlib.abc.FileLoader
helps
write a loader that uses the file system as the storage mechanism for a module’s
code. The loader for source files
(importlib.machinery.SourceFileLoader
), sourceless bytecode files
(importlib.machinery.SourcelessFileLoader
), and extension modules
(importlib.machinery.ExtensionFileLoader
) are now available for
direct use.
ImportError
now has name
and path
attributes which are set when
there is relevant data to provide. The message for failed imports will also
provide the full name of the module now instead of just the tail end of the
module’s name.
The importlib.invalidate_caches()
function will now call the method with
the same name on all finders cached in sys.path_importer_cache
to help
clean up any stored state as necessary.
Visible Changes¶
For potential required changes to code, see the Porting Python code section.
Beyond the expanse of what importlib
now exposes, there are other
visible changes to import. The biggest is that sys.meta_path
and
sys.path_hooks
now store all of the meta path finders and path entry
hooks used by import. Previously the finders were implicit and hidden within
the C code of import instead of being directly exposed. This means that one can
now easily remove or change the order of the various finders to fit one’s needs.
Another change is that all modules have a __loader__
attribute, storing the
loader used to create the module. PEP 302 has been updated to make this
attribute mandatory for loaders to implement, so in the future once 3rd-party
loaders have been updated people will be able to rely on the existence of the
attribute. Until such time, though, import is setting the module post-load.
Loaders are also now expected to set the __package__
attribute from
PEP 366. Once again, import itself is already setting this on all loaders
from importlib
and import itself is setting the attribute post-load.
None
is now inserted into sys.path_importer_cache
when no finder
can be found on sys.path_hooks
. Since imp.NullImporter
is not
directly exposed on sys.path_hooks
it could no longer be relied upon to
always be available to use as a value representing no finder found.
All other changes relate to semantic changes which should be taken into consideration when updating code for Python 3.3, and thus should be read about in the Porting Python code section of this document.
(Implementation by Brett Cannon)
Other Language Changes¶
Some smaller changes made to the core Python language are:
Added support for Unicode name aliases and named sequences. Both
unicodedata.lookup()
and'\N{...}'
now resolve name aliases, andunicodedata.lookup()
resolves named sequences too.(Contributed by Ezio Melotti in bpo-12753.)
Unicode database updated to UCD version 6.1.0
Equality comparisons on
range()
objects now return a result reflecting the equality of the underlying sequences generated by those range objects. (bpo-13201)The
count()
,find()
,rfind()
,index()
andrindex()
methods ofbytes
andbytearray
objects now accept an integer between 0 and 255 as their first argument.(Contributed by Petri Lehtinen in bpo-12170.)
The
rjust()
,ljust()
, andcenter()
methods ofbytes
andbytearray
now accept abytearray
for thefill
argument. (Contributed by Petri Lehtinen in bpo-12380.)New methods have been added to
list
andbytearray
:copy()
andclear()
(bpo-10516). Consequently,MutableSequence
now also defines aclear()
method (bpo-11388).Raw bytes literals can now be written
rb"..."
as well asbr"..."
.(Contributed by Antoine Pitrou in bpo-13748.)
dict.setdefault()
now does only one lookup for the given key, making it atomic when used with built-in types.(Contributed by Filip Gruszczyński in bpo-13521.)
The error messages produced when a function call does not match the function signature have been significantly improved.
(Contributed by Benjamin Peterson.)
A Finer-Grained Import Lock¶
Previous versions of CPython have always relied on a global import lock.
This led to unexpected annoyances, such as deadlocks when importing a module
would trigger code execution in a different thread as a side-effect.
Clumsy workarounds were sometimes employed, such as the
PyImport_ImportModuleNoBlock()
C API function.
In Python 3.3, importing a module takes a per-module lock. This correctly serializes importation of a given module from multiple threads (preventing the exposure of incompletely initialized modules), while eliminating the aforementioned annoyances.
(Contributed by Antoine Pitrou in bpo-9260.)
Builtin functions and types¶
open()
gets a new opener parameter: the underlying file descriptor for the file object is then obtained by calling opener with (file, flags). It can be used to use custom flags likeos.O_CLOEXEC
for example. The'x'
mode was added: open for exclusive creation, failing if the file already exists.print()
: added the flush keyword argument. If the flush keyword argument is true, the stream is forcibly flushed.hash()
: hash randomization is enabled by default, seeobject.__hash__()
andPYTHONHASHSEED
.The
str
type gets a newcasefold()
method: return a casefolded copy of the string, casefolded strings may be used for caseless matching. For example,'ß'.casefold()
returns'ss'
.The sequence documentation has been substantially rewritten to better explain the binary/text sequence distinction and to provide specific documentation sections for the individual builtin sequence types (bpo-4966).
New Modules¶
faulthandler¶
This new debug module faulthandler
contains functions to dump Python tracebacks explicitly,
on a fault (a crash like a segmentation fault), after a timeout, or on a user
signal. Call faulthandler.enable()
to install fault handlers for the
SIGSEGV
, SIGFPE
, SIGABRT
,
SIGBUS
, and SIGILL
signals.
You can also enable them at startup by setting the PYTHONFAULTHANDLER
environment variable or by using -X
faulthandler
command line option.
Example of a segmentation fault on Linux:
$ python -q -X faulthandler
>>> import ctypes
>>> ctypes.string_at(0)
Fatal Python error: Segmentation fault
Current thread 0x00007fb899f39700:
File "/home/python/cpython/Lib/ctypes/__init__.py", line 486 in string_at
File "<stdin>", line 1 in <module>
Segmentation fault
ipaddress¶
The new ipaddress
module provides tools for creating and manipulating
objects representing IPv4 and IPv6 addresses, networks and interfaces (i.e.
an IP address associated with a specific IP subnet).
(Contributed by Google and Peter Moody in PEP 3144.)
lzma¶
The newly added lzma
module provides data compression and decompression
using the LZMA algorithm, including support for the .xz
and .lzma
file formats.
(Contributed by Nadeem Vawda and Per Øyvind Karlsen in bpo-6715.)
Improved Modules¶
abc¶
Improved support for abstract base classes containing descriptors composed with
abstract methods. The recommended approach to declaring abstract descriptors is
now to provide __isabstractmethod__
as a dynamically updated
property. The built-in descriptors have been updated accordingly.
abc.abstractproperty
has been deprecated, useproperty
withabc.abstractmethod()
instead.abc.abstractclassmethod
has been deprecated, useclassmethod
withabc.abstractmethod()
instead.abc.abstractstaticmethod
has been deprecated, usestaticmethod
withabc.abstractmethod()
instead.
(Contributed by Darren Dale in bpo-11610.)
abc.ABCMeta.register()
now returns the registered subclass, which means
it can now be used as a class decorator (bpo-10868).
array¶
The array
module supports the long long type using q
and
Q
type codes.
(Contributed by Oren Tirosh and Hirokazu Yamamoto in bpo-1172711.)
base64¶
ASCII-only Unicode strings are now accepted by the decoding functions of the
base64
modern interface. For example, base64.b64decode('YWJj')
returns b'abc'
. (Contributed by Catalin Iacob in bpo-13641.)
binascii¶
In addition to the binary objects they normally accept, the a2b_
functions
now all also accept ASCII-only strings as input. (Contributed by Antoine
Pitrou in bpo-13637.)
bz2¶
The bz2
module has been rewritten from scratch. In the process, several
new features have been added:
New
bz2.open()
function: open a bzip2-compressed file in binary or text mode.bz2.BZ2File
can now read from and write to arbitrary file-like objects, by means of its constructor’s fileobj argument.(Contributed by Nadeem Vawda in bpo-5863.)
bz2.BZ2File
andbz2.decompress()
can now decompress multi-stream inputs (such as those produced by the pbzip2 tool).bz2.BZ2File
can now also be used to create this type of file, using the'a'
(append) mode.(Contributed by Nir Aides in bpo-1625.)
bz2.BZ2File
now implements all of theio.BufferedIOBase
API, except for thedetach()
andtruncate()
methods.
codecs¶
The mbcs
codec has been rewritten to handle correctly
replace
and ignore
error handlers on all Windows versions. The
mbcs
codec now supports all error handlers, instead of only
replace
to encode and ignore
to decode.
A new Windows-only codec has been added: cp65001
(bpo-13216). It is the
Windows code page 65001 (Windows UTF-8, CP_UTF8
). For example, it is used
by sys.stdout
if the console output code page is set to cp65001 (e.g., using
chcp 65001
command).
Multibyte CJK decoders now resynchronize faster. They only ignore the first
byte of an invalid byte sequence. For example, b'\xff\n'.decode('gb2312',
'replace')
now returns a \n
after the replacement character.
Incremental CJK codec encoders are no longer reset at each call to their encode() methods. For example:
>>> import codecs
>>> encoder = codecs.getincrementalencoder('hz')('strict')
>>> b''.join(encoder.encode(x) for x in '\u52ff\u65bd\u65bc\u4eba\u3002 Bye.')
b'~{NpJ)l6HK!#~} Bye.'
This example gives b'~{Np~}~{J)~}~{l6~}~{HK~}~{!#~} Bye.'
with older Python
versions.
The unicode_internal
codec has been deprecated.
collections¶
Addition of a new ChainMap
class to allow treating a
number of mappings as a single unit. (Written by Raymond Hettinger for
bpo-11089, made public in bpo-11297.)
The abstract base classes have been moved in a new collections.abc
module, to better differentiate between the abstract and the concrete
collections classes. Aliases for ABCs are still present in the
collections
module to preserve existing imports. (bpo-11085)
The Counter
class now supports the unary +
and -
operators, as well as the in-place operators +=
, -=
, |=
, and
&=
. (Contributed by Raymond Hettinger in bpo-13121.)
contextlib¶
ExitStack
now provides a solid foundation for
programmatic manipulation of context managers and similar cleanup
functionality. Unlike the previous contextlib.nested
API (which was
deprecated and removed), the new API is designed to work correctly
regardless of whether context managers acquire their resources in
their __init__
method (for example, file objects) or in their
__enter__
method (for example, synchronisation objects from the
threading
module).
crypt¶
Addition of salt and modular crypt format (hashing method) and the mksalt()
function to the crypt
module.
curses¶
If the
curses
module is linked to the ncursesw library, use Unicode functions when Unicode strings or characters are passed (e.g.waddwstr()
), and bytes functions otherwise (e.g.waddstr()
).Use the locale encoding instead of
utf-8
to encode Unicode strings.curses.window
has a newcurses.window.encoding
attribute.The
curses.window
class has a newget_wch()
method to get a wide characterThe
curses
module has a newunget_wch()
function to push a wide character so the nextget_wch()
will return it
(Contributed by Iñigo Serna in bpo-6755.)
datetime¶
Equality comparisons between naive and aware
datetime
instances now returnFalse
instead of raisingTypeError
(bpo-15006).New
datetime.datetime.timestamp()
method: Return POSIX timestamp corresponding to thedatetime
instance.The
datetime.datetime.strftime()
method supports formatting years older than 1000.The
datetime.datetime.astimezone()
method can now be called without arguments to convert datetime instance to the system timezone.
decimal¶
- bpo-7652 - integrate fast native decimal arithmetic.
C-module and libmpdec written by Stefan Krah.
The new C version of the decimal module integrates the high speed libmpdec library for arbitrary precision correctly rounded decimal floating-point arithmetic. libmpdec conforms to IBM’s General Decimal Arithmetic Specification.
Performance gains range from 10x for database applications to 100x for numerically intensive applications. These numbers are expected gains for standard precisions used in decimal floating-point arithmetic. Since the precision is user configurable, the exact figures may vary. For example, in integer bignum arithmetic the differences can be significantly higher.
The following table is meant as an illustration. Benchmarks are available at https://www.bytereef.org/mpdecimal/quickstart.html.
decimal.py
_decimal
speedup
pi
42.02s
0.345s
120x
telco
172.19s
5.68s
30x
psycopg
3.57s
0.29s
12x
Features¶
The
FloatOperation
signal optionally enables stricter semantics for mixing floats and Decimals.If Python is compiled without threads, the C version automatically disables the expensive thread local context machinery. In this case, the variable
HAVE_THREADS
is set toFalse
.
API changes¶
The C module has the following context limits, depending on the machine architecture:
In the context templates (
DefaultContext
,BasicContext
andExtendedContext
) the magnitude ofEmax
andEmin
has changed to999999
.The
Decimal
constructor in decimal.py does not observe the context limits and converts values with arbitrary exponents or precision exactly. Since the C version has internal limits, the following scheme is used: If possible, values are converted exactly, otherwiseInvalidOperation
is raised and the result is NaN. In the latter case it is always possible to usecreate_decimal()
in order to obtain a rounded or inexact value.The power function in decimal.py is always correctly rounded. In the C version, it is defined in terms of the correctly rounded
exp()
andln()
functions, but the final result is only “almost always correctly rounded”.In the C version, the context dictionary containing the signals is a
MutableMapping
. For speed reasons,flags
andtraps
always refer to the sameMutableMapping
that the context was initialized with. If a new signal dictionary is assigned,flags
andtraps
are updated with the new values, but they do not reference the RHS dictionary.Pickling a
Context
produces a different output in order to have a common interchange format for the Python and C versions.The order of arguments in the
Context
constructor has been changed to match the order displayed byrepr()
.The
watchexp
parameter in thequantize()
method is deprecated.
email¶
Policy Framework¶
The email package now has a policy
framework. A
Policy
is an object with several methods and properties
that control how the email package behaves. The primary policy for Python 3.3
is the Compat32
policy, which provides backward
compatibility with the email package in Python 3.2. A policy
can be
specified when an email message is parsed by a parser
, or when a
Message
object is created, or when an email is
serialized using a generator
. Unless overridden, a policy passed
to a parser
is inherited by all the Message
object and sub-objects
created by the parser
. By default a generator
will use the policy of
the Message
object it is serializing. The default policy is
compat32
.
The minimum set of controls implemented by all policy
objects are:
max_line_length |
The maximum length, excluding the linesep character(s),
individual lines may have when a |
linesep |
The character used to separate individual lines when a
|
cte_type |
|
raise_on_defect |
Causes a |
A new policy instance, with new settings, is created using the
clone()
method of policy objects. clone
takes
any of the above controls as keyword arguments. Any control not specified in
the call retains its default value. Thus you can create a policy that uses
\r\n
linesep characters like this:
mypolicy = compat32.clone(linesep='\r\n')
Policies can be used to make the generation of messages in the format needed by
your application simpler. Instead of having to remember to specify
linesep='\r\n'
in all the places you call a generator
, you can specify
it once, when you set the policy used by the parser
or the Message
,
whichever your program uses to create Message
objects. On the other hand,
if you need to generate messages in multiple forms, you can still specify the
parameters in the appropriate generator
call. Or you can have custom
policy instances for your different cases, and pass those in when you create
the generator
.
Provisional Policy with New Header API¶
While the policy framework is worthwhile all by itself, the main motivation for introducing it is to allow the creation of new policies that implement new features for the email package in a way that maintains backward compatibility for those who do not use the new policies. Because the new policies introduce a new API, we are releasing them in Python 3.3 as a provisional policy. Backwards incompatible changes (up to and including removal of the code) may occur if deemed necessary by the core developers.
The new policies are instances of EmailPolicy
,
and add the following additional controls:
refold_source |
Controls whether or not headers parsed by a
|
header_factory |
A callable that take a |
The header_factory
is the key to the new features provided by the new
policies. When one of the new policies is used, any header retrieved from
a Message
object is an object produced by the header_factory
, and any
time you set a header on a Message
it becomes an object produced by
header_factory
. All such header objects have a name
attribute equal
to the header name. Address and Date headers have additional attributes
that give you access to the parsed data of the header. This means you can now
do things like this:
>>> m = Message(policy=SMTP)
>>> m['To'] = 'Éric <foo@example.com>'
>>> m['to']
'Éric <foo@example.com>'
>>> m['to'].addresses
(Address(display_name='Éric', username='foo', domain='example.com'),)
>>> m['to'].addresses[0].username
'foo'
>>> m['to'].addresses[0].display_name
'Éric'
>>> m['Date'] = email.utils.localtime()
>>> m['Date'].datetime
datetime.datetime(2012, 5, 25, 21, 39, 24, 465484, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000), 'EDT'))
>>> m['Date']
'Fri, 25 May 2012 21:44:27 -0400'
>>> print(m)
To: =?utf-8?q?=C3=89ric?= <foo@example.com>
Date: Fri, 25 May 2012 21:44:27 -0400
You will note that the unicode display name is automatically encoded as
utf-8
when the message is serialized, but that when the header is accessed
directly, you get the unicode version. This eliminates any need to deal with
the email.header
decode_header()
or
make_header()
functions.
You can also create addresses from parts:
>>> m['cc'] = [Group('pals', [Address('Bob', 'bob', 'example.com'),
... Address('Sally', 'sally', 'example.com')]),
... Address('Bonzo', addr_spec='bonz@laugh.com')]
>>> print(m)
To: =?utf-8?q?=C3=89ric?= <foo@example.com>
Date: Fri, 25 May 2012 21:44:27 -0400
cc: pals: Bob <bob@example.com>, Sally <sally@example.com>;, Bonzo <bonz@laugh.com>
Decoding to unicode is done automatically:
>>> m2 = message_from_string(str(m))
>>> m2['to']
'Éric <foo@example.com>'
When you parse a message, you can use the addresses
and groups
attributes of the header objects to access the groups and individual
addresses:
>>> m2['cc'].addresses
(Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com'), Address(display_name='Bonzo', username='bonz', domain='laugh.com'))
>>> m2['cc'].groups
(Group(display_name='pals', addresses=(Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com')), Group(display_name=None, addresses=(Address(display_name='Bonzo', username='bonz', domain='laugh.com'),))
In summary, if you use one of the new policies, header manipulation works the way it ought to: your application works with unicode strings, and the email package transparently encodes and decodes the unicode to and from the RFC standard Content Transfer Encodings.
Other API Changes¶
New BytesHeaderParser
, added to the parser
module to complement HeaderParser
and complete the Bytes
API.
New utility functions:
format_datetime()
: given adatetime
, produce a string formatted for use in an email header.parsedate_to_datetime()
: given a date string from an email header, convert it into an awaredatetime
, or a naivedatetime
if the offset is-0000
.localtime()
: With no argument, returns the current local time as an awaredatetime
using the localtimezone
. Given an awaredatetime
, converts it into an awaredatetime
using the localtimezone
.
ftplib¶
ftplib.FTP
now accepts asource_address
keyword argument to specify the(host, port)
to use as the source address in the bind call when creating the outgoing socket. (Contributed by Giampaolo Rodolà in bpo-8594.)The
FTP_TLS
class now provides a newccc()
function to revert control channel back to plaintext. This can be useful to take advantage of firewalls that know how to handle NAT with non-secure FTP without opening fixed ports. (Contributed by Giampaolo Rodolà in bpo-12139.)Added
ftplib.FTP.mlsd()
method which provides a parsable directory listing format and deprecatesftplib.FTP.nlst()
andftplib.FTP.dir()
. (Contributed by Giampaolo Rodolà in bpo-11072.)
functools¶
The functools.lru_cache()
decorator now accepts a typed
keyword
argument (that defaults to False
to ensure that it caches values of
different types that compare equal in separate cache slots. (Contributed
by Raymond Hettinger in bpo-13227.)
gc¶
It is now possible to register callbacks invoked by the garbage collector
before and after collection using the new callbacks
list.
hmac¶
A new compare_digest()
function has been added to prevent side
channel attacks on digests through timing analysis. (Contributed by Nick
Coghlan and Christian Heimes in bpo-15061.)
http¶
http.server.BaseHTTPRequestHandler
now buffers the headers and writes
them all at once when end_headers()
is
called. A new method flush_headers()
can be used to directly manage when the accumulated headers are sent.
(Contributed by Andrew Schaaf in bpo-3709.)
http.server
now produces valid HTML 4.01 strict
output.
(Contributed by Ezio Melotti in bpo-13295.)
http.client.HTTPResponse
now has a
readinto()
method, which means it can be used
as an io.RawIOBase
class. (Contributed by John Kuhn in
bpo-13464.)
html¶
html.parser.HTMLParser
is now able to parse broken markup without
raising errors, therefore the strict argument of the constructor and the
HTMLParseError
exception are now deprecated.
The ability to parse broken markup is the result of a number of bug fixes that
are also available on the latest bug fix releases of Python 2.7/3.2.
(Contributed by Ezio Melotti in bpo-15114, and bpo-14538,
bpo-13993, bpo-13960, bpo-13358, bpo-1745761,
bpo-755670, bpo-13357, bpo-12629, bpo-1200313,
bpo-670664, bpo-13273, bpo-12888, bpo-7311.)
A new html5
dictionary that maps HTML5 named character
references to the equivalent Unicode character(s) (e.g. html5['gt;'] ==
'>'
) has been added to the html.entities
module. The dictionary is
now also used by HTMLParser
. (Contributed by Ezio
Melotti in bpo-11113 and bpo-15156.)
imaplib¶
The IMAP4_SSL
constructor now accepts an SSLContext
parameter to control parameters of the secure channel.
(Contributed by Sijin Joseph in bpo-8808.)
inspect¶
A new getclosurevars()
function has been added. This function
reports the current binding of all names referenced from the function body and
where those names were resolved, making it easier to verify correct internal
state when testing code that relies on stateful closures.
(Contributed by Meador Inge and Nick Coghlan in bpo-13062.)
A new getgeneratorlocals()
function has been added. This
function reports the current binding of local variables in the generator’s
stack frame, making it easier to verify correct internal state when testing
generators.
(Contributed by Meador Inge in bpo-15153.)
io¶
The open()
function has a new 'x'
mode that can be used to
exclusively create a new file, and raise a FileExistsError
if the file
already exists. It is based on the C11 ‘x’ mode to fopen().
(Contributed by David Townshend in bpo-12760.)
The constructor of the TextIOWrapper
class has a new
write_through optional argument. If write_through is True
, calls to
write()
are guaranteed not to be buffered: any data
written on the TextIOWrapper
object is immediately handled to its
underlying binary buffer.
itertools¶
accumulate()
now takes an optional func
argument for
providing a user-supplied binary function.
logging¶
The basicConfig()
function now supports an optional handlers
argument taking an iterable of handlers to be added to the root logger.
A class level attribute append_nul
has
been added to SysLogHandler
to allow control of the
appending of the NUL
(\000
) byte to syslog records, since for some
daemons it is required while for others it is passed through to the log.
math¶
The math
module has a new function, log2()
, which returns
the base-2 logarithm of x.
(Written by Mark Dickinson in bpo-11888.)
mmap¶
The read()
method is now more compatible with other file-like
objects: if the argument is omitted or specified as None
, it returns the
bytes from the current file position to the end of the mapping. (Contributed
by Petri Lehtinen in bpo-12021.)
multiprocessing¶
The new multiprocessing.connection.wait()
function allows polling
multiple objects (such as connections, sockets and pipes) with a timeout.
(Contributed by Richard Oudkerk in bpo-12328.)
multiprocessing.connection.Connection
objects can now be transferred
over multiprocessing connections.
(Contributed by Richard Oudkerk in bpo-4892.)
multiprocessing.Process
now accepts a daemon
keyword argument
to override the default behavior of inheriting the daemon
flag from
the parent process (bpo-6064).
New attribute multiprocessing.Process.sentinel
allows a
program to wait on multiple Process
objects at one
time using the appropriate OS primitives (for example, select
on
posix systems).
New methods multiprocessing.pool.Pool.starmap()
and
starmap_async()
provide
itertools.starmap()
equivalents to the existing
multiprocessing.pool.Pool.map()
and
map_async()
functions. (Contributed by Hynek
Schlawack in bpo-12708.)
nntplib¶
The nntplib.NNTP
class now supports the context management protocol to
unconditionally consume socket.error
exceptions and to close the NNTP
connection when done:
>>> from nntplib import NNTP
>>> with NNTP('news.gmane.org') as n:
... n.group('gmane.comp.python.committers')
...
('211 1755 1 1755 gmane.comp.python.committers', 1755, 1, 1755, 'gmane.comp.python.committers')
>>>
(Contributed by Giampaolo Rodolà in bpo-9795.)
os¶
The
os
module has a newpipe2()
function that makes it possible to create a pipe withO_CLOEXEC
orO_NONBLOCK
flags set atomically. This is especially useful to avoid race conditions in multi-threaded programs.The
os
module has a newsendfile()
function which provides an efficient “zero-copy” way for copying data from one file (or socket) descriptor to another. The phrase “zero-copy” refers to the fact that all of the copying of data between the two descriptors is done entirely by the kernel, with no copying of data into userspace buffers.sendfile()
can be used to efficiently copy data from a file on disk to a network socket, e.g. for downloading a file.(Patch submitted by Ross Lagerwall and Giampaolo Rodolà in bpo-10882.)
To avoid race conditions like symlink attacks and issues with temporary files and directories, it is more reliable (and also faster) to manipulate file descriptors instead of file names. Python 3.3 enhances existing functions and introduces new functions to work on file descriptors (bpo-4761, bpo-10755 and bpo-14626).
The
os
module has a newfwalk()
function similar towalk()
except that it also yields file descriptors referring to the directories visited. This is especially useful to avoid symlink races.The following functions get new optional dir_fd (paths relative to directory descriptors) and/or follow_symlinks (not following symlinks):
access()
,chflags()
,chmod()
,chown()
,link()
,lstat()
,mkdir()
,mkfifo()
,mknod()
,open()
,readlink()
,remove()
,rename()
,replace()
,rmdir()
,stat()
,symlink()
,unlink()
,utime()
. Platform support for using these parameters can be checked via the setsos.supports_dir_fd
andos.supports_follow_symlinks
.The following functions now support a file descriptor for their path argument:
chdir()
,chmod()
,chown()
,execve()
,listdir()
,pathconf()
,exists()
,stat()
,statvfs()
,utime()
. Platform support for this can be checked via theos.supports_fd
set.
access()
accepts aneffective_ids
keyword argument to turn on using the effective uid/gid rather than the real uid/gid in the access check. Platform support for this can be checked via thesupports_effective_ids
set.The
os
module has two new functions:getpriority()
andsetpriority()
. They can be used to get or set process niceness/priority in a fashion similar toos.nice()
but extended to all processes instead of just the current one.(Patch submitted by Giampaolo Rodolà in bpo-10784.)
The new
os.replace()
function allows cross-platform renaming of a file with overwriting the destination. Withos.rename()
, an existing destination file is overwritten under POSIX, but raises an error under Windows. (Contributed by Antoine Pitrou in bpo-8828.)The stat family of functions (
stat()
,fstat()
, andlstat()
) now support reading a file’s timestamps with nanosecond precision. Symmetrically,utime()
can now write file timestamps with nanosecond precision. (Contributed by Larry Hastings in bpo-14127.)The new
os.get_terminal_size()
function queries the size of the terminal attached to a file descriptor. See alsoshutil.get_terminal_size()
. (Contributed by Zbigniew Jędrzejewski-Szmek in bpo-13609.)
New functions to support Linux extended attributes (bpo-12720):
getxattr()
,listxattr()
,removexattr()
,setxattr()
.New interface to the scheduler. These functions control how a process is allocated CPU time by the operating system. New functions:
sched_get_priority_max()
,sched_get_priority_min()
,sched_getaffinity()
,sched_getparam()
,sched_getscheduler()
,sched_rr_get_interval()
,sched_setaffinity()
,sched_setparam()
,sched_setscheduler()
,sched_yield()
,New functions to control the file system:
posix_fadvise()
: Announces an intention to access data in a specific pattern thus allowing the kernel to make optimizations.posix_fallocate()
: Ensures that enough disk space is allocated for a file.sync()
: Force write of everything to disk.
Additional new posix functions:
lockf()
: Apply, test or remove a POSIX lock on an open file descriptor.pread()
: Read from a file descriptor at an offset, the file offset remains unchanged.pwrite()
: Write to a file descriptor from an offset, leaving the file offset unchanged.readv()
: Read from a file descriptor into a number of writable buffers.truncate()
: Truncate the file corresponding to path, so that it is at most length bytes in size.waitid()
: Wait for the completion of one or more child processes.writev()
: Write the contents of buffers to a file descriptor, where buffers is an arbitrary sequence of buffers.getgrouplist()
(bpo-9344): Return list of group ids that specified user belongs to.
times()
anduname()
: Return type changed from a tuple to a tuple-like object with named attributes.Some platforms now support additional constants for the
lseek()
function, such asos.SEEK_HOLE
andos.SEEK_DATA
.New constants
RTLD_LAZY
,RTLD_NOW
,RTLD_GLOBAL
,RTLD_LOCAL
,RTLD_NODELETE
,RTLD_NOLOAD
, andRTLD_DEEPBIND
are available on platforms that support them. These are for use with thesys.setdlopenflags()
function, and supersede the similar constants defined inctypes
andDLFCN
. (Contributed by Victor Stinner in bpo-13226.)os.symlink()
now accepts (and ignores) thetarget_is_directory
keyword argument on non-Windows platforms, to ease cross-platform support.
pdb¶
Tab-completion is now available not only for command names, but also their
arguments. For example, for the break
command, function and file names
are completed.
(Contributed by Georg Brandl in bpo-14210)
pickle¶
pickle.Pickler
objects now have an optional
dispatch_table
attribute allowing per-pickler
reduction functions to be set.
(Contributed by Richard Oudkerk in bpo-14166.)
pydoc¶
The Tk GUI and the serve()
function have been removed from the
pydoc
module: pydoc -g
and serve()
have been deprecated
in Python 3.2.
re¶
str
regular expressions now support \u
and \U
escapes.
(Contributed by Serhiy Storchaka in bpo-3665.)
sched¶
run()
now accepts a blocking parameter which when set to false makes the method execute the scheduled events due to expire soonest (if any) and then return immediately. This is useful in case you want to use thescheduler
in non-blocking applications. (Contributed by Giampaolo Rodolà in bpo-13449.)scheduler
class can now be safely used in multi-threaded environments. (Contributed by Josiah Carlson and Giampaolo Rodolà in bpo-8684.)timefunc and delayfunct parameters of
scheduler
class constructor are now optional and defaults totime.time()
andtime.sleep()
respectively. (Contributed by Chris Clark in bpo-13245.)enter()
andenterabs()
argument parameter is now optional. (Contributed by Chris Clark in bpo-13245.)enter()
andenterabs()
now accept a kwargs parameter. (Contributed by Chris Clark in bpo-13245.)
select¶
Solaris and derivative platforms have a new class select.devpoll
for high performance asynchronous sockets via /dev/poll
.
(Contributed by Jesús Cea Avión in bpo-6397.)
shlex¶
The previously undocumented helper function quote
from the
pipes
modules has been moved to the shlex
module and
documented. quote()
properly escapes all characters in a string
that might be otherwise given special meaning by the shell.
shutil¶
New functions:
disk_usage()
: provides total, used and free disk space statistics. (Contributed by Giampaolo Rodolà in bpo-12442.)chown()
: allows one to change user and/or group of the given path also specifying the user/group names and not only their numeric ids. (Contributed by Sandro Tosi in bpo-12191.)shutil.get_terminal_size()
: returns the size of the terminal window to which the interpreter is attached. (Contributed by Zbigniew Jędrzejewski-Szmek in bpo-13609.)
copy2()
andcopystat()
now preserve file timestamps with nanosecond precision on platforms that support it. They also preserve file “extended attributes” on Linux. (Contributed by Larry Hastings in bpo-14127 and bpo-15238.)Several functions now take an optional
symlinks
argument: when that parameter is true, symlinks aren’t dereferenced and the operation instead acts on the symlink itself (or creates one, if relevant). (Contributed by Hynek Schlawack in bpo-12715.)When copying files to a different file system,
move()
now handles symlinks the way the posixmv
command does, recreating the symlink rather than copying the target file contents. (Contributed by Jonathan Niehof in bpo-9993.)move()
now also returns thedst
argument as its result.rmtree()
is now resistant to symlink attacks on platforms which support the newdir_fd
parameter inos.open()
andos.unlink()
. (Contributed by Martin von Löwis and Hynek Schlawack in bpo-4489.)
signal¶
The
signal
module has new functions:pthread_sigmask()
: fetch and/or change the signal mask of the calling thread (Contributed by Jean-Paul Calderone in bpo-8407);pthread_kill()
: send a signal to a thread;sigpending()
: examine pending functions;sigwait()
: wait a signal;sigwaitinfo()
: wait for a signal, returning detailed information about it;sigtimedwait()
: likesigwaitinfo()
but with a timeout.
The signal handler writes the signal number as a single byte instead of a nul byte into the wakeup file descriptor. So it is possible to wait more than one signal and know which signals were raised.
signal.signal()
andsignal.siginterrupt()
raise an OSError, instead of a RuntimeError: OSError has an errno attribute.
smtpd¶
The smtpd
module now supports RFC 5321 (extended SMTP) and RFC 1870
(size extension). Per the standard, these extensions are enabled if and only
if the client initiates the session with an EHLO
command.
(Initial ELHO
support by Alberto Trevino. Size extension by Juhana
Jauhiainen. Substantial additional work on the patch contributed by Michele
Orrù and Dan Boswell. bpo-8739)
smtplib¶
The SMTP
, SMTP_SSL
, and
LMTP
classes now accept a source_address
keyword argument
to specify the (host, port)
to use as the source address in the bind call
when creating the outgoing socket. (Contributed by Paulo Scardine in
bpo-11281.)
SMTP
now supports the context management protocol, allowing an
SMTP
instance to be used in a with
statement. (Contributed
by Giampaolo Rodolà in bpo-11289.)
The SMTP_SSL
constructor and the starttls()
method now accept an SSLContext parameter to control parameters of the secure
channel. (Contributed by Kasun Herath in bpo-8809.)
socket¶
The
socket
class now exposes additional methods to process ancillary data when supported by the underlying platform:(Contributed by David Watson in bpo-6560, based on an earlier patch by Heiko Wundram)
The
socket
class now supports the PF_CAN protocol family (https://en.wikipedia.org/wiki/Socketcan), on Linux (https://lwn.net/Articles/253425).(Contributed by Matthias Fuchs, updated by Tiago Gonçalves in bpo-10141.)
The
socket
class now supports the PF_RDS protocol family (https://en.wikipedia.org/wiki/Reliable_Datagram_Sockets and https://oss.oracle.com/projects/rds).The
socket
class now supports thePF_SYSTEM
protocol family on OS X. (Contributed by Michael Goderbauer in bpo-13777.)New function
sethostname()
allows the hostname to be set on Unix systems if the calling process has sufficient privileges. (Contributed by Ross Lagerwall in bpo-10866.)
socketserver¶
BaseServer
now has an overridable method
service_actions()
that is called by the
serve_forever()
method in the service loop.
ForkingMixIn
now uses this to clean up zombie
child processes. (Contributed by Justin Warkentin in bpo-11109.)
sqlite3¶
New sqlite3.Connection
method
set_trace_callback()
can be used to capture a trace of
all sql commands processed by sqlite. (Contributed by Torsten Landschoff
in bpo-11688.)
ssl¶
The
ssl
module has two new random generation functions:RAND_bytes()
: generate cryptographically strong pseudo-random bytes.RAND_pseudo_bytes()
: generate pseudo-random bytes.
(Contributed by Victor Stinner in bpo-12049.)
The
ssl
module now exposes a finer-grained exception hierarchy in order to make it easier to inspect the various kinds of errors. (Contributed by Antoine Pitrou in bpo-11183.)load_cert_chain()
now accepts a password argument to be used if the private key is encrypted. (Contributed by Adam Simpkins in bpo-12803.)Diffie-Hellman key exchange, both regular and Elliptic Curve-based, is now supported through the
load_dh_params()
andset_ecdh_curve()
methods. (Contributed by Antoine Pitrou in bpo-13626 and bpo-13627.)SSL sockets have a new
get_channel_binding()
method allowing the implementation of certain authentication mechanisms such as SCRAM-SHA-1-PLUS. (Contributed by Jacek Konieczny in bpo-12551.)You can query the SSL compression algorithm used by an SSL socket, thanks to its new
compression()
method. The new attributeOP_NO_COMPRESSION
can be used to disable compression. (Contributed by Antoine Pitrou in bpo-13634.)Support has been added for the Next Protocol Negotiation extension using the
ssl.SSLContext.set_npn_protocols()
method. (Contributed by Colin Marc in bpo-14204.)SSL errors can now be introspected more easily thanks to
library
andreason
attributes. (Contributed by Antoine Pitrou in bpo-14837.)The
get_server_certificate()
function now supports IPv6. (Contributed by Charles-François Natali in bpo-11811.)New attribute
OP_CIPHER_SERVER_PREFERENCE
allows setting SSLv3 server sockets to use the server’s cipher ordering preference rather than the client’s (bpo-13635).
stat¶
The undocumented tarfile.filemode function has been moved to
stat.filemode()
. It can be used to convert a file’s mode to a string of
the form ‘-rwxrwxrwx’.
(Contributed by Giampaolo Rodolà in bpo-14807.)
struct¶
The struct
module now supports ssize_t
and size_t
via the
new codes n
and N
, respectively. (Contributed by Antoine Pitrou
in bpo-3163.)
subprocess¶
Command strings can now be bytes objects on posix platforms. (Contributed by Victor Stinner in bpo-8513.)
A new constant DEVNULL
allows suppressing output in a
platform-independent fashion. (Contributed by Ross Lagerwall in
bpo-5870.)
sys¶
The sys
module has a new thread_info
named
tuple holding information about the thread implementation
(bpo-11223).
tarfile¶
tarfile
now supports lzma
encoding via the lzma
module.
(Contributed by Lars Gustäbel in bpo-5689.)
tempfile¶
tempfile.SpooledTemporaryFile
's truncate()
method now accepts
a size
parameter. (Contributed by Ryan Kelly in bpo-9957.)
textwrap¶
The textwrap
module has a new indent()
that makes
it straightforward to add a common prefix to selected lines in a block
of text (bpo-13857).
threading¶
threading.Condition
, threading.Semaphore
,
threading.BoundedSemaphore
, threading.Event
, and
threading.Timer
, all of which used to be factory functions returning a
class instance, are now classes and may be subclassed. (Contributed by Éric
Araujo in bpo-10968.)
The threading.Thread
constructor now accepts a daemon
keyword
argument to override the default behavior of inheriting the daemon
flag
value from the parent thread (bpo-6064).
The formerly private function _thread.get_ident
is now available as the
public function threading.get_ident()
. This eliminates several cases of
direct access to the _thread
module in the stdlib. Third party code that
used _thread.get_ident
should likewise be changed to use the new public
interface.
time¶
The PEP 418 added new functions to the time
module:
get_clock_info()
: Get information on a clock.monotonic()
: Monotonic clock (cannot go backward), not affected by system clock updates.perf_counter()
: Performance counter with the highest available resolution to measure a short duration.process_time()
: Sum of the system and user CPU time of the current process.
Other new functions:
clock_getres()
,clock_gettime()
andclock_settime()
functions withCLOCK_xxx
constants. (Contributed by Victor Stinner in bpo-10278.)
To improve cross platform consistency, sleep()
now raises a
ValueError
when passed a negative sleep value. Previously this was an
error on posix, but produced an infinite sleep on Windows.
types¶
Add a new types.MappingProxyType
class: Read-only proxy of a mapping.
(bpo-14386)
The new functions types.new_class()
and types.prepare_class()
provide support
for PEP 3115 compliant dynamic type creation. (bpo-14588)
unittest¶
assertRaises()
, assertRaisesRegex()
, assertWarns()
, and
assertWarnsRegex()
now accept a keyword argument msg when used as
context managers. (Contributed by Ezio Melotti and Winston Ewert in
bpo-10775.)
unittest.TestCase.run()
now returns the TestResult
object.
urllib¶
The Request
class, now accepts a method argument
used by get_method()
to determine what HTTP method
should be used. For example, this will send a 'HEAD'
request:
>>> urlopen(Request('https://www.python.org', method='HEAD'))
webbrowser¶
The webbrowser
module supports more “browsers”: Google Chrome (named
chrome, chromium, chrome-browser or
chromium-browser depending on the version and operating system),
and the generic launchers xdg-open, from the FreeDesktop.org
project, and gvfs-open, which is the default URI handler for GNOME
3. (The former contributed by Arnaud Calmettes in bpo-13620, the latter
by Matthias Klose in bpo-14493.)
xml.etree.ElementTree¶
The xml.etree.ElementTree
module now imports its C accelerator by
default; there is no longer a need to explicitly import
xml.etree.cElementTree
(this module stays for backwards compatibility,
but is now deprecated). In addition, the iter
family of methods of
Element
has been optimized (rewritten in C).
The module’s documentation has also been greatly improved with added examples
and a more detailed reference.
zlib¶
New attribute zlib.Decompress.eof
makes it possible to distinguish
between a properly formed compressed stream and an incomplete or truncated one.
(Contributed by Nadeem Vawda in bpo-12646.)
New attribute zlib.ZLIB_RUNTIME_VERSION
reports the version string of
the underlying zlib
library that is loaded at runtime. (Contributed by
Torsten Landschoff in bpo-12306.)
Optimizations¶
Major performance enhancements have been added:
Thanks to PEP 393, some operations on Unicode strings have been optimized:
the memory footprint is divided by 2 to 4 depending on the text
encode an ASCII string to UTF-8 doesn’t need to encode characters anymore, the UTF-8 representation is shared with the ASCII representation
the UTF-8 encoder has been optimized
repeating a single ASCII letter and getting a substring of an ASCII string is 4 times faster
UTF-8 is now 2x to 4x faster. UTF-16 encoding is now up to 10x faster.
(Contributed by Serhiy Storchaka, bpo-14624, bpo-14738 and bpo-15026.)
Build and C API Changes¶
Changes to Python’s build process and to the C API include:
New PEP 3118 related function:
PEP 393 added new Unicode types, macros and functions:
High-level API:
Low-level API:
PyASCIIObject
andPyCompactUnicodeObject
structuresPyUnicode_DATA
,PyUnicode_1BYTE_DATA
,PyUnicode_2BYTE_DATA
,PyUnicode_4BYTE_DATA
PyUnicode_KIND
withPyUnicode_Kind
enum:PyUnicode_WCHAR_KIND
,PyUnicode_1BYTE_KIND
,PyUnicode_2BYTE_KIND
,PyUnicode_4BYTE_KIND
PyArg_ParseTuple
now accepts abytearray
for thec
format (bpo-12380).
Deprecated¶
Unsupported Operating Systems¶
OS/2 and VMS are no longer supported due to the lack of a maintainer.
Windows 2000 and Windows platforms which set COMSPEC
to command.com
are no longer supported due to maintenance burden.
OSF support, which was deprecated in 3.2, has been completely removed.
Deprecated Python modules, functions and methods¶
Passing a non-empty string to
object.__format__()
is deprecated, and will produce aTypeError
in Python 3.4 (bpo-9856).The
unicode_internal
codec has been deprecated because of the PEP 393, use UTF-8, UTF-16 (utf-16-le
orutf-16-be
), or UTF-32 (utf-32-le
orutf-32-be
)ftplib.FTP.nlst()
andftplib.FTP.dir()
: useftplib.FTP.mlsd()
platform.popen()
: use thesubprocess
module. Check especially the Replacing Older Functions with the subprocess Module section (bpo-11377).bpo-13374: The Windows bytes API has been deprecated in the
os
module. Use Unicode filenames, instead of bytes filenames, to not depend on the ANSI code page anymore and to support any filename.bpo-13988: The
xml.etree.cElementTree
module is deprecated. The accelerator is used automatically whenever available.The behaviour of
time.clock()
depends on the platform: use the newtime.perf_counter()
ortime.process_time()
function instead, depending on your requirements, to have a well defined behaviour.The
os.stat_float_times()
function is deprecated.abc
module:abc.abstractproperty
has been deprecated, useproperty
withabc.abstractmethod()
instead.abc.abstractclassmethod
has been deprecated, useclassmethod
withabc.abstractmethod()
instead.abc.abstractstaticmethod
has been deprecated, usestaticmethod
withabc.abstractmethod()
instead.
importlib
package:importlib.abc.SourceLoader.path_mtime()
is now deprecated in favour ofimportlib.abc.SourceLoader.path_stats()
as bytecode files now store both the modification time and size of the source file the bytecode file was compiled from.
Deprecated functions and types of the C API¶
The Py_UNICODE
has been deprecated by PEP 393 and will be
removed in Python 4. All functions using this type are deprecated:
Unicode functions and methods using Py_UNICODE
and
Py_UNICODE* types:
PyUnicode_FromUnicode
: usePyUnicode_FromWideChar()
orPyUnicode_FromKindAndData()
PyUnicode_AS_UNICODE
,PyUnicode_AsUnicode()
,PyUnicode_AsUnicodeAndSize()
: usePyUnicode_AsWideCharString()
PyUnicode_AS_DATA
: usePyUnicode_DATA
withPyUnicode_READ
andPyUnicode_WRITE
PyUnicode_GET_SIZE
,PyUnicode_GetSize()
: usePyUnicode_GET_LENGTH
orPyUnicode_GetLength()
PyUnicode_GET_DATA_SIZE
: usePyUnicode_GET_LENGTH(str) * PyUnicode_KIND(str)
(only work on ready strings)PyUnicode_AsUnicodeCopy()
: usePyUnicode_AsUCS4Copy()
orPyUnicode_AsWideCharString()
PyUnicode_GetMax()
Functions and macros manipulating Py_UNICODE* strings:
Py_UNICODE_strlen()
: usePyUnicode_GetLength()
orPyUnicode_GET_LENGTH
Py_UNICODE_strcat()
: usePyUnicode_CopyCharacters()
orPyUnicode_FromFormat()
Py_UNICODE_strcpy()
,Py_UNICODE_strncpy()
,Py_UNICODE_COPY()
: usePyUnicode_CopyCharacters()
orPyUnicode_Substring()
Py_UNICODE_strcmp()
: usePyUnicode_Compare()
Py_UNICODE_strncmp()
: usePyUnicode_Tailmatch()
Py_UNICODE_strchr()
,Py_UNICODE_strrchr()
: usePyUnicode_FindChar()
Py_UNICODE_FILL()
: usePyUnicode_Fill()
Py_UNICODE_MATCH
Encoders:
PyUnicode_Encode()
: usePyUnicode_AsEncodedObject()
PyUnicode_EncodeUTF7()
PyUnicode_EncodeUTF8()
: usePyUnicode_AsUTF8()
orPyUnicode_AsUTF8String()
PyUnicode_EncodeUTF32()
PyUnicode_EncodeUTF16()
PyUnicode_EncodeUnicodeEscape()
usePyUnicode_AsUnicodeEscapeString()
PyUnicode_EncodeRawUnicodeEscape()
usePyUnicode_AsRawUnicodeEscapeString()
PyUnicode_EncodeLatin1()
: usePyUnicode_AsLatin1String()
PyUnicode_EncodeASCII()
: usePyUnicode_AsASCIIString()
PyUnicode_EncodeCharmap()
PyUnicode_TranslateCharmap()
PyUnicode_EncodeMBCS()
: usePyUnicode_AsMBCSString()
orPyUnicode_EncodeCodePage()
(withCP_ACP
code_page)PyUnicode_EncodeDecimal()
,PyUnicode_TransformDecimalToASCII()
Deprecated features¶
The array
module’s 'u'
format code is now deprecated and will be
removed in Python 4 together with the rest of the (Py_UNICODE
) API.
Porting to Python 3.3¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Porting Python code¶
Hash randomization is enabled by default. Set the
PYTHONHASHSEED
environment variable to0
to disable hash randomization. See also theobject.__hash__()
method.bpo-12326: On Linux, sys.platform doesn’t contain the major version anymore. It is now always ‘linux’, instead of ‘linux2’ or ‘linux3’ depending on the Linux version used to build Python. Replace sys.platform == ‘linux2’ with sys.platform.startswith(‘linux’), or directly sys.platform == ‘linux’ if you don’t need to support older Python versions.
bpo-13847, bpo-14180:
time
anddatetime
:OverflowError
is now raised instead ofValueError
if a timestamp is out of range.OSError
is now raised if C functionsgmtime()
orlocaltime()
failed.The default finders used by import now utilize a cache of what is contained within a specific directory. If you create a Python source file or sourceless bytecode file, make sure to call
importlib.invalidate_caches()
to clear out the cache for the finders to notice the new file.ImportError
now uses the full name of the module that was attempted to be imported. Doctests that check ImportErrors’ message will need to be updated to use the full name of the module instead of just the tail of the name.The index argument to
__import__()
now defaults to 0 instead of -1 and no longer support negative values. It was an oversight when PEP 328 was implemented that the default value remained -1. If you need to continue to perform a relative import followed by an absolute import, then perform the relative import using an index of 1, followed by another import using an index of 0. It is preferred, though, that you useimportlib.import_module()
rather than call__import__()
directly.__import__()
no longer allows one to use an index value other than 0 for top-level modules. E.g.__import__('sys', level=1)
is now an error.Because
sys.meta_path
andsys.path_hooks
now have finders on them by default, you will most likely want to uselist.insert()
instead oflist.append()
to add to those lists.Because
None
is now inserted intosys.path_importer_cache
, if you are clearing out entries in the dictionary of paths that do not have a finder, you will need to remove keys paired with values ofNone
andimp.NullImporter
to be backwards-compatible. This will lead to extra overhead on older versions of Python that re-insertNone
intosys.path_importer_cache
where it represents the use of implicit finders, but semantically it should not change anything.importlib.abc.Finder
no longer specifies afind_module()
abstract method that must be implemented. If you were relying on subclasses to implement that method, make sure to check for the method’s existence first. You will probably want to check forfind_loader()
first, though, in the case of working with path entry finders.pkgutil
has been converted to useimportlib
internally. This eliminates many edge cases where the old behaviour of the PEP 302 import emulation failed to match the behaviour of the real import system. The import emulation itself is still present, but is now deprecated. Thepkgutil.iter_importers()
andpkgutil.walk_packages()
functions special case the standard import hooks so they are still supported even though they do not provide the non-standarditer_modules()
method.A longstanding RFC-compliance bug (bpo-1079) in the parsing done by
email.header.decode_header()
has been fixed. Code that uses the standard idiom to convert encoded headers into unicode (str(make_header(decode_header(h))
) will see no change, but code that looks at the individual tuples returned by decode_header will see that whitespace that precedes or followsASCII
sections is now included in theASCII
section. Code that builds headers usingmake_header
should also continue to work without change, sincemake_header
continues to add whitespace betweenASCII
and non-ASCII
sections if it is not already present in the input strings.email.utils.formataddr()
now does the correct content transfer encoding when passed non-ASCII
display names. Any code that depended on the previous buggy behavior that preserved the non-ASCII
unicode in the formatted output string will need to be changed (bpo-1690608).poplib.POP3.quit()
may now raise protocol errors like all otherpoplib
methods. Code that assumesquit
does not raisepoplib.error_proto
errors may need to be changed if errors onquit
are encountered by a particular application (bpo-11291).The
strict
argument toemail.parser.Parser
, deprecated since Python 2.4, has finally been removed.The deprecated method
unittest.TestCase.assertSameElements
has been removed.The deprecated variable
time.accept2dyear
has been removed.The deprecated
Context._clamp
attribute has been removed from thedecimal
module. It was previously replaced by the public attributeclamp
. (See bpo-8540.)The undocumented internal helper class
SSLFakeFile
has been removed fromsmtplib
, since its functionality has long been provided directly bysocket.socket.makefile()
.Passing a negative value to
time.sleep()
on Windows now raises an error instead of sleeping forever. It has always raised an error on posix.The
ast.__version__
constant has been removed. If you need to make decisions affected by the AST version, usesys.version_info
to make the decision.Code that used to work around the fact that the
threading
module used factory functions by subclassing the private classes will need to change to subclass the now-public classes.The undocumented debugging machinery in the threading module has been removed, simplifying the code. This should have no effect on production code, but is mentioned here in case any application debug frameworks were interacting with it (bpo-13550).
Porting C code¶
In the course of changes to the buffer API the undocumented
smalltable
member of thePy_buffer
structure has been removed and the layout of thePyMemoryViewObject
has changed.All extensions relying on the relevant parts in
memoryobject.h
orobject.h
must be rebuilt.Due to PEP 393, the
Py_UNICODE
type and all functions using this type are deprecated (but will stay available for at least five years). If you were using low-level Unicode APIs to construct and access unicode objects and you want to benefit of the memory footprint reduction provided by PEP 393, you have to convert your code to the new Unicode API.However, if you only have been using high-level functions such as
PyUnicode_Concat()
,PyUnicode_Join()
orPyUnicode_FromFormat()
, your code will automatically take advantage of the new unicode representations.PyImport_GetMagicNumber()
now returns-1
upon failure.As a negative value for the level argument to
__import__()
is no longer valid, the same now holds forPyImport_ImportModuleLevel()
. This also means that the value of level used byPyImport_ImportModuleEx()
is now0
instead of-1
.
Building C extensions¶
The range of possible file names for C extensions has been narrowed. Very rarely used spellings have been suppressed: under POSIX, files named
xxxmodule.so
,xxxmodule.abi3.so
andxxxmodule.cpython-*.so
are no longer recognized as implementing thexxx
module. If you had been generating such files, you have to switch to the other spellings (i.e., remove themodule
string from the file names).(implemented in bpo-14040.)
Command Line Switch Changes¶
The -Q command-line flag and related artifacts have been removed. Code checking sys.flags.division_warning will need updating.
(bpo-10998, contributed by Éric Araujo.)
When python is started with
-S
,import site
will no longer add site-specific paths to the module search paths. In previous versions, it did.(bpo-11591, contributed by Carl Meyer with editions by Éric Araujo.)

File
, line
, in
File
, line
, in
:
File
, line
, in
:
File
, line
, in
File
, line
, in
: