python_doc_md/Intermediate/library/bdb.md

# `!bdb`{.interpreted-text role="mod"} \-\-- Debugger framework

::: {.module synopsis="Debugger framework."}
bdb
:::

**Source code:** `Lib/bdb.py`{.interpreted-text role="source"}

------------------------------------------------------------------------

The `!bdb`{.interpreted-text role="mod"} module handles basic debugger functions, like setting breakpoints or managing execution via the debugger.

The following exception is defined:

::: exception
BdbQuit

Exception raised by the `Bdb`{.interpreted-text role="class"} class for quitting the debugger.
:::

The `!bdb`{.interpreted-text role="mod"} module also defines two classes:

::::::::::::::::::: {.Breakpoint(self, .file, .line, .temporary=False, .cond=None, .funcname=None)}
This class implements temporary breakpoints, ignore counts, disabling and (re-)enabling, and conditionals.

Breakpoints are indexed by number through a list called `bpbynumber`{.interpreted-text role="attr"} and by `(file, line)` pairs through `bplist`{.interpreted-text role="attr"}. The former points to a single instance of class `Breakpoint`{.interpreted-text role="class"}. The latter points to a list of such instances since there may be more than one breakpoint per line.

When creating a breakpoint, its associated `file name <file>`{.interpreted-text role="attr"} should be in canonical form. If a `funcname`{.interpreted-text role="attr"} is defined, a breakpoint `hit <hits>`{.interpreted-text role="attr"} will be counted when the first line of that function is executed. A `conditional <cond>`{.interpreted-text role="attr"} breakpoint always counts a `hit <hits>`{.interpreted-text role="attr"}.

`Breakpoint`{.interpreted-text role="class"} instances have the following methods:

::: method
deleteMe()

Delete the breakpoint from the list associated to a file/line. If it is the last breakpoint in that position, it also deletes the entry for the file/line.
:::

::: method
enable()

Mark the breakpoint as enabled.
:::

::: method
disable()

Mark the breakpoint as disabled.
:::

:::: method
bpformat()

Return a string with all the information about the breakpoint, nicely formatted:

- Breakpoint number.
- Temporary status (del or keep).
- File/line position.
- Break condition.
- Number of times to ignore.
- Number of times hit.

::: versionadded
3.2
:::
::::

::: method
bpprint(out=None)

Print the output of `bpformat`{.interpreted-text role="meth"} to the file *out*, or if it is `None`, to standard output.
:::

`Breakpoint`{.interpreted-text role="class"} instances have the following attributes:

::: attribute
file

File name of the `Breakpoint`{.interpreted-text role="class"}.
:::

::: attribute
line

Line number of the `Breakpoint`{.interpreted-text role="class"} within `file`{.interpreted-text role="attr"}.
:::

::: attribute
temporary

`True` if a `Breakpoint`{.interpreted-text role="class"} at (file, line) is temporary.
:::

::: attribute
cond

Condition for evaluating a `Breakpoint`{.interpreted-text role="class"} at (file, line).
:::

::: attribute
funcname

Function name that defines whether a `Breakpoint`{.interpreted-text role="class"} is hit upon entering the function.
:::

::: attribute
enabled

`True` if `Breakpoint`{.interpreted-text role="class"} is enabled.
:::

::: attribute
bpbynumber

Numeric index for a single instance of a `Breakpoint`{.interpreted-text role="class"}.
:::

::: attribute
bplist

Dictionary of `Breakpoint`{.interpreted-text role="class"} instances indexed by (`file`{.interpreted-text role="attr"}, `line`{.interpreted-text role="attr"}) tuples.
:::

::: attribute
ignore

Number of times to ignore a `Breakpoint`{.interpreted-text role="class"}.
:::

::: attribute
hits

Count of the number of times a `Breakpoint`{.interpreted-text role="class"} has been hit.
:::
:::::::::::::::::::

::::::::::::::::::::::::::::::::::::::::::::::::::::::: {.Bdb(skip=None, .backend='settrace')}
The `Bdb`{.interpreted-text role="class"} class acts as a generic Python debugger base class.

This class takes care of the details of the trace facility; a derived class should implement user interaction. The standard debugger class (`pdb.Pdb`{.interpreted-text role="class"}) is an example.

The *skip* argument, if given, must be an iterable of glob-style module name patterns. The debugger will not step into frames that originate in a module that matches one of these patterns. Whether a frame is considered to originate in a certain module is determined by the `__name__` in the frame globals.

The *backend* argument specifies the backend to use for `Bdb`{.interpreted-text role="class"}. It can be either `'settrace'` or `'monitoring'`. `'settrace'` uses `sys.settrace`{.interpreted-text role="func"} which has the best backward compatibility. The `'monitoring'` backend uses the new `sys.monitoring`{.interpreted-text role="mod"} that was introduced in Python 3.12, which can be much more efficient because it can disable unused events. We are trying to keep the exact interfaces for both backends, but there are some differences. The debugger developers are encouraged to use the `'monitoring'` backend to achieve better performance.

::: versionchanged
3.1 Added the *skip* parameter.
:::

::: versionchanged
3.14 Added the *backend* parameter.
:::

The following methods of `Bdb`{.interpreted-text role="class"} normally don\'t need to be overridden.

::: method
canonic(filename)

Return canonical form of *filename*.

For real file names, the canonical form is an operating-system-dependent, `case-normalized <os.path.normcase>`{.interpreted-text role="func"} `absolute path
<os.path.abspath>`{.interpreted-text role="func"}. A *filename* with angle brackets, such as `"<stdin>"` generated in interactive mode, is returned unchanged.
:::

:::: method
start_trace(self)

Start tracing. For `'settrace'` backend, this method is equivalent to `sys.settrace(self.trace_dispatch)`

::: versionadded
3.14
:::
::::

:::: method
stop_trace(self)

Stop tracing. For `'settrace'` backend, this method is equivalent to `sys.settrace(None)`

::: versionadded
3.14
:::
::::

::: method
reset()

Set the `!botframe`{.interpreted-text role="attr"}, `!stopframe`{.interpreted-text role="attr"}, `!returnframe`{.interpreted-text role="attr"} and `quitting <Bdb.set_quit>`{.interpreted-text role="attr"} attributes with values ready to start debugging.
:::

::: method
trace_dispatch(frame, event, arg)

This function is installed as the trace function of debugged frames. Its return value is the new trace function (in most cases, that is, itself).

The default implementation decides how to dispatch a frame, depending on the type of event (passed as a string) that is about to be executed. *event* can be one of the following:

- `"line"`: A new line of code is going to be executed.
- `"call"`: A function is about to be called, or another code block entered.
- `"return"`: A function or other code block is about to return.
- `"exception"`: An exception has occurred.

For all the events, specialized functions (see below) are called.

The *arg* parameter depends on the previous event.

See the documentation for `sys.settrace`{.interpreted-text role="func"} for more information on the trace function. For more information on code and frame objects, refer to `types`{.interpreted-text role="ref"}.
:::

::: method
dispatch_line(frame)

If the debugger should stop on the current line, invoke the `user_line`{.interpreted-text role="meth"} method (which should be overridden in subclasses). Raise a `BdbQuit`{.interpreted-text role="exc"} exception if the `quitting  <Bdb.set_quit>`{.interpreted-text role="attr"} flag is set (which can be set from `user_line`{.interpreted-text role="meth"}). Return a reference to the `trace_dispatch`{.interpreted-text role="meth"} method for further tracing in that scope.
:::

::: method
dispatch_call(frame, arg)

If the debugger should stop on this function call, invoke the `user_call`{.interpreted-text role="meth"} method (which should be overridden in subclasses). Raise a `BdbQuit`{.interpreted-text role="exc"} exception if the `quitting  <Bdb.set_quit>`{.interpreted-text role="attr"} flag is set (which can be set from `user_call`{.interpreted-text role="meth"}). Return a reference to the `trace_dispatch`{.interpreted-text role="meth"} method for further tracing in that scope.
:::

::: method
dispatch_return(frame, arg)

If the debugger should stop on this function return, invoke the `user_return`{.interpreted-text role="meth"} method (which should be overridden in subclasses). Raise a `BdbQuit`{.interpreted-text role="exc"} exception if the `quitting  <Bdb.set_quit>`{.interpreted-text role="attr"} flag is set (which can be set from `user_return`{.interpreted-text role="meth"}). Return a reference to the `trace_dispatch`{.interpreted-text role="meth"} method for further tracing in that scope.
:::

::: method
dispatch_exception(frame, arg)

If the debugger should stop at this exception, invokes the `user_exception`{.interpreted-text role="meth"} method (which should be overridden in subclasses). Raise a `BdbQuit`{.interpreted-text role="exc"} exception if the `quitting  <Bdb.set_quit>`{.interpreted-text role="attr"} flag is set (which can be set from `user_exception`{.interpreted-text role="meth"}). Return a reference to the `trace_dispatch`{.interpreted-text role="meth"} method for further tracing in that scope.
:::

Normally derived classes don\'t override the following methods, but they may if they want to redefine the definition of stopping and breakpoints.

::: method
is_skipped_module(module_name)

Return `True` if *module_name* matches any skip pattern.
:::

::: method
stop_here(frame)

Return `True` if *frame* is below the starting frame in the stack.
:::

::: method
break_here(frame)

Return `True` if there is an effective breakpoint for this line.

Check whether a line or function breakpoint exists and is in effect. Delete temporary breakpoints based on information from `effective`{.interpreted-text role="func"}.
:::

::: method
break_anywhere(frame)

Return `True` if any breakpoint exists for *frame*\'s filename.
:::

Derived classes should override these methods to gain control over debugger operation.

::: method
user_call(frame, argument_list)

Called from `dispatch_call`{.interpreted-text role="meth"} if a break might stop inside the called function.

*argument_list* is not used anymore and will always be `None`. The argument is kept for backwards compatibility.
:::

::: method
user_line(frame)

Called from `dispatch_line`{.interpreted-text role="meth"} when either `stop_here`{.interpreted-text role="meth"} or `break_here`{.interpreted-text role="meth"} returns `True`.
:::

::: method
user_return(frame, return_value)

Called from `dispatch_return`{.interpreted-text role="meth"} when `stop_here`{.interpreted-text role="meth"} returns `True`.
:::

::: method
user_exception(frame, exc_info)

Called from `dispatch_exception`{.interpreted-text role="meth"} when `stop_here`{.interpreted-text role="meth"} returns `True`.
:::

::: method
do_clear(arg)

Handle how a breakpoint must be removed when it is a temporary one.

This method must be implemented by derived classes.
:::

Derived classes and clients can call the following methods to affect the stepping state.

::: method
set_step()

Stop after one line of code.
:::

::: method
set_next(frame)

Stop on the next line in or below the given frame.
:::

::: method
set_return(frame)

Stop when returning from the given frame.
:::

::: method
set_until(frame, lineno=None)

Stop when the line with the *lineno* greater than the current one is reached or when returning from current frame.
:::

:::: method
set_trace(\[frame\])

Start debugging from *frame*. If *frame* is not specified, debugging starts from caller\'s frame.

::: versionchanged
3.13 `set_trace`{.interpreted-text role="func"} will enter the debugger immediately, rather than on the next line of code to be executed.
:::
::::

::: method
set_continue()

Stop only at breakpoints or when finished. If there are no breakpoints, set the system trace function to `None`.
:::

:::: method
set_quit()

::: index
single: quitting (bdb.Bdb attribute)
:::

Set the `!quitting`{.interpreted-text role="attr"} attribute to `True`. This raises `BdbQuit`{.interpreted-text role="exc"} in the next call to one of the `!dispatch_\*`{.interpreted-text role="meth"} methods.
::::

Derived classes and clients can call the following methods to manipulate breakpoints. These methods return a string containing an error message if something went wrong, or `None` if all is well.

::: method
set_break(filename, lineno, temporary=False, cond=None, funcname=None)

Set a new breakpoint. If the *lineno* line doesn\'t exist for the *filename* passed as argument, return an error message. The *filename* should be in canonical form, as described in the `canonic`{.interpreted-text role="meth"} method.
:::

::: method
clear_break(filename, lineno)

Delete the breakpoints in *filename* and *lineno*. If none were set, return an error message.
:::

::: method
clear_bpbynumber(arg)

Delete the breakpoint which has the index *arg* in the `Breakpoint.bpbynumber`{.interpreted-text role="attr"}. If *arg* is not numeric or out of range, return an error message.
:::

::: method
clear_all_file_breaks(filename)

Delete all breakpoints in *filename*. If none were set, return an error message.
:::

::: method
clear_all_breaks()

Delete all existing breakpoints. If none were set, return an error message.
:::

:::: method
get_bpbynumber(arg)

Return a breakpoint specified by the given number. If *arg* is a string, it will be converted to a number. If *arg* is a non-numeric string, if the given breakpoint never existed or has been deleted, a `ValueError`{.interpreted-text role="exc"} is raised.

::: versionadded
3.2
:::
::::

::: method
get_break(filename, lineno)

Return `True` if there is a breakpoint for *lineno* in *filename*.
:::

::: method
get_breaks(filename, lineno)

Return all breakpoints for *lineno* in *filename*, or an empty list if none are set.
:::

::: method
get_file_breaks(filename)

Return all breakpoints in *filename*, or an empty list if none are set.
:::

::: method
get_all_breaks()

Return all breakpoints that are set.
:::

Derived classes and clients can call the following methods to disable and restart events to achieve better performance. These methods only work when using the `'monitoring'` backend.

:::: method
disable_current_event()

Disable the current event until the next time `restart_events`{.interpreted-text role="func"} is called. This is helpful when the debugger is not interested in the current line.

::: versionadded
3.14
:::
::::

:::: method
restart_events()

Restart all the disabled events. This function is automatically called in `dispatch_*` methods after `user_*` methods are called. If the `dispatch_*` methods are not overridden, the disabled events will be restarted after each user interaction.

::: versionadded
3.14
:::
::::

Derived classes and clients can call the following methods to get a data structure representing a stack trace.

::: method
get_stack(f, t)

Return a list of (frame, lineno) tuples in a stack trace, and a size.

The most recently called frame is last in the list. The size is the number of frames below the frame where the debugger was invoked.
:::

::: method
format_stack_entry(frame_lineno, lprefix=\': \')

Return a string with information about a stack entry, which is a `(frame, lineno)` tuple. The return string contains:

- The canonical filename which contains the frame.
- The function name or `"<lambda>"`.
- The input arguments.
- The return value.
- The line of code (if it exists).
:::

The following two methods can be called by clients to use a debugger to debug a `statement`{.interpreted-text role="term"}, given as a string.

::: method
run(cmd, globals=None, locals=None)

Debug a statement executed via the `exec`{.interpreted-text role="func"} function. *globals* defaults to `!__main__.__dict__`{.interpreted-text role="attr"}, *locals* defaults to *globals*.
:::

::: method
runeval(expr, globals=None, locals=None)

Debug an expression executed via the `eval`{.interpreted-text role="func"} function. *globals* and *locals* have the same meaning as in `run`{.interpreted-text role="meth"}.
:::

::: method
runctx(cmd, globals, locals)

For backwards compatibility. Calls the `run`{.interpreted-text role="meth"} method.
:::

::: method
runcall(func, /, *args,*\*kwds)

Debug a single function call, and return its result.
:::
:::::::::::::::::::::::::::::::::::::::::::::::::::::::

Finally, the module defines the following functions:

::: function
checkfuncname(b, frame)

Return `True` if we should break here, depending on the way the `Breakpoint`{.interpreted-text role="class"} *b* was set.

If it was set via line number, it checks if `b.line <bdb.Breakpoint.line>`{.interpreted-text role="attr"} is the same as the one in *frame*. If the breakpoint was set via `function name <bdb.Breakpoint.funcname>`{.interpreted-text role="attr"}, we have to check we are in the right *frame* (the right function) and if we are on its first executable line.
:::

::: function
effective(file, line, frame)

Return `(active breakpoint, delete temporary flag)` or `(None, None)` as the breakpoint to act upon.

The *active breakpoint* is the first entry in `bplist <bdb.Breakpoint.bplist>`{.interpreted-text role="attr"} for the (`file <bdb.Breakpoint.file>`{.interpreted-text role="attr"}, `line <bdb.Breakpoint.line>`{.interpreted-text role="attr"}) (which must exist) that is `enabled <bdb.Breakpoint.enabled>`{.interpreted-text role="attr"}, for which `checkfuncname`{.interpreted-text role="func"} is true, and that has neither a false `condition <bdb.Breakpoint.cond>`{.interpreted-text role="attr"} nor positive `ignore <bdb.Breakpoint.ignore>`{.interpreted-text role="attr"} count. The *flag*, meaning that a temporary breakpoint should be deleted, is `False` only when the `cond <bdb.Breakpoint.cond>`{.interpreted-text role="attr"} cannot be evaluated (in which case, `ignore <bdb.Breakpoint.ignore>`{.interpreted-text role="attr"} count is ignored).

If no such entry exists, then `(None, None)` is returned.
:::

::: function
set_trace()

Start debugging with a `Bdb`{.interpreted-text role="class"} instance from caller\'s frame.
:::