mirror of
https://github.com/python/cpython.git
synced 2024-12-16 13:25:18 +08:00
548 lines
20 KiB
ReStructuredText
548 lines
20 KiB
ReStructuredText
.. _debugger:
|
|
|
|
:mod:`pdb` --- The Python Debugger
|
|
==================================
|
|
|
|
.. module:: pdb
|
|
:synopsis: The Python debugger for interactive interpreters.
|
|
|
|
**Source code:** :source:`Lib/pdb.py`
|
|
|
|
.. index:: single: debugging
|
|
|
|
--------------
|
|
|
|
The module :mod:`pdb` defines an interactive source code debugger for Python
|
|
programs. It supports setting (conditional) breakpoints and single stepping at
|
|
the source line level, inspection of stack frames, source code listing, and
|
|
evaluation of arbitrary Python code in the context of any stack frame. It also
|
|
supports post-mortem debugging and can be called under program control.
|
|
|
|
.. index::
|
|
single: Pdb (class in pdb)
|
|
module: bdb
|
|
module: cmd
|
|
|
|
The debugger is extensible -- it is actually defined as the class :class:`Pdb`.
|
|
This is currently undocumented but easily understood by reading the source. The
|
|
extension interface uses the modules :mod:`bdb` and :mod:`cmd`.
|
|
|
|
The debugger's prompt is ``(Pdb)``. Typical usage to run a program under control
|
|
of the debugger is::
|
|
|
|
>>> import pdb
|
|
>>> import mymodule
|
|
>>> pdb.run('mymodule.test()')
|
|
> <string>(0)?()
|
|
(Pdb) continue
|
|
> <string>(1)?()
|
|
(Pdb) continue
|
|
NameError: 'spam'
|
|
> <string>(1)?()
|
|
(Pdb)
|
|
|
|
.. versionchanged:: 3.3
|
|
Tab-completion via the :mod:`readline` module is available for commands and
|
|
command arguments, e.g. the current global and local names are offered as
|
|
arguments of the ``p`` command.
|
|
|
|
:file:`pdb.py` can also be invoked as a script to debug other scripts. For
|
|
example::
|
|
|
|
python3 -m pdb myscript.py
|
|
|
|
When invoked as a script, pdb will automatically enter post-mortem debugging if
|
|
the program being debugged exits abnormally. After post-mortem debugging (or
|
|
after normal exit of the program), pdb will restart the program. Automatic
|
|
restarting preserves pdb's state (such as breakpoints) and in most cases is more
|
|
useful than quitting the debugger upon program's exit.
|
|
|
|
.. versionadded:: 3.2
|
|
:file:`pdb.py` now accepts a ``-c`` option that executes commands as if given
|
|
in a :file:`.pdbrc` file, see :ref:`debugger-commands`.
|
|
|
|
.. versionadded:: 3.7
|
|
:file:`pdb.py` now accepts a ``-m`` option that execute modules similar to the way
|
|
``python3 -m`` does. As with a script, the debugger will pause execution just
|
|
before the first line of the module.
|
|
|
|
|
|
The typical usage to break into the debugger from a running program is to
|
|
insert ::
|
|
|
|
import pdb; pdb.set_trace()
|
|
|
|
at the location you want to break into the debugger. You can then step through
|
|
the code following this statement, and continue running without the debugger
|
|
using the :pdbcmd:`continue` command.
|
|
|
|
.. versionadded:: 3.7
|
|
The built-in :func:`breakpoint()`, when called with defaults, can be used
|
|
instead of ``import pdb; pdb.set_trace()``.
|
|
|
|
The typical usage to inspect a crashed program is::
|
|
|
|
>>> import pdb
|
|
>>> import mymodule
|
|
>>> mymodule.test()
|
|
Traceback (most recent call last):
|
|
File "<stdin>", line 1, in <module>
|
|
File "./mymodule.py", line 4, in test
|
|
test2()
|
|
File "./mymodule.py", line 3, in test2
|
|
print(spam)
|
|
NameError: spam
|
|
>>> pdb.pm()
|
|
> ./mymodule.py(3)test2()
|
|
-> print(spam)
|
|
(Pdb)
|
|
|
|
|
|
The module defines the following functions; each enters the debugger in a
|
|
slightly different way:
|
|
|
|
.. function:: run(statement, globals=None, locals=None)
|
|
|
|
Execute the *statement* (given as a string or a code object) under debugger
|
|
control. The debugger prompt appears before any code is executed; you can
|
|
set breakpoints and type :pdbcmd:`continue`, or you can step through the
|
|
statement using :pdbcmd:`step` or :pdbcmd:`next` (all these commands are
|
|
explained below). The optional *globals* and *locals* arguments specify the
|
|
environment in which the code is executed; by default the dictionary of the
|
|
module :mod:`__main__` is used. (See the explanation of the built-in
|
|
:func:`exec` or :func:`eval` functions.)
|
|
|
|
|
|
.. function:: runeval(expression, globals=None, locals=None)
|
|
|
|
Evaluate the *expression* (given as a string or a code object) under debugger
|
|
control. When :func:`runeval` returns, it returns the value of the
|
|
expression. Otherwise this function is similar to :func:`run`.
|
|
|
|
|
|
.. function:: runcall(function, *args, **kwds)
|
|
|
|
Call the *function* (a function or method object, not a string) with the
|
|
given arguments. When :func:`runcall` returns, it returns whatever the
|
|
function call returned. The debugger prompt appears as soon as the function
|
|
is entered.
|
|
|
|
|
|
.. function:: set_trace(*, header=None)
|
|
|
|
Enter the debugger at the calling stack frame. This is useful to hard-code
|
|
a breakpoint at a given point in a program, even if the code is not
|
|
otherwise being debugged (e.g. when an assertion fails). If given,
|
|
*header* is printed to the console just before debugging begins.
|
|
|
|
.. versionchanged:: 3.7
|
|
The keyword-only argument *header*.
|
|
|
|
|
|
.. function:: post_mortem(traceback=None)
|
|
|
|
Enter post-mortem debugging of the given *traceback* object. If no
|
|
*traceback* is given, it uses the one of the exception that is currently
|
|
being handled (an exception must be being handled if the default is to be
|
|
used).
|
|
|
|
|
|
.. function:: pm()
|
|
|
|
Enter post-mortem debugging of the traceback found in
|
|
:data:`sys.last_traceback`.
|
|
|
|
|
|
The ``run*`` functions and :func:`set_trace` are aliases for instantiating the
|
|
:class:`Pdb` class and calling the method of the same name. If you want to
|
|
access further features, you have to do this yourself:
|
|
|
|
.. class:: Pdb(completekey='tab', stdin=None, stdout=None, skip=None, \
|
|
nosigint=False, readrc=True)
|
|
|
|
:class:`Pdb` is the debugger class.
|
|
|
|
The *completekey*, *stdin* and *stdout* arguments are passed to the
|
|
underlying :class:`cmd.Cmd` class; see the description there.
|
|
|
|
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. [1]_
|
|
|
|
By default, Pdb sets a handler for the SIGINT signal (which is sent when the
|
|
user presses :kbd:`Ctrl-C` on the console) when you give a ``continue`` command.
|
|
This allows you to break into the debugger again by pressing :kbd:`Ctrl-C`. If you
|
|
want Pdb not to touch the SIGINT handler, set *nosigint* to true.
|
|
|
|
The *readrc* argument defaults to true and controls whether Pdb will load
|
|
.pdbrc files from the filesystem.
|
|
|
|
Example call to enable tracing with *skip*::
|
|
|
|
import pdb; pdb.Pdb(skip=['django.*']).set_trace()
|
|
|
|
.. audit-event:: pdb.Pdb "" pdb.Pdb
|
|
|
|
.. versionadded:: 3.1
|
|
The *skip* argument.
|
|
|
|
.. versionadded:: 3.2
|
|
The *nosigint* argument. Previously, a SIGINT handler was never set by
|
|
Pdb.
|
|
|
|
.. versionchanged:: 3.6
|
|
The *readrc* argument.
|
|
|
|
.. method:: run(statement, globals=None, locals=None)
|
|
runeval(expression, globals=None, locals=None)
|
|
runcall(function, *args, **kwds)
|
|
set_trace()
|
|
|
|
See the documentation for the functions explained above.
|
|
|
|
|
|
.. _debugger-commands:
|
|
|
|
Debugger Commands
|
|
-----------------
|
|
|
|
The commands recognized by the debugger are listed below. Most commands can be
|
|
abbreviated to one or two letters as indicated; e.g. ``h(elp)`` means that
|
|
either ``h`` or ``help`` can be used to enter the help command (but not ``he``
|
|
or ``hel``, nor ``H`` or ``Help`` or ``HELP``). Arguments to commands must be
|
|
separated by whitespace (spaces or tabs). Optional arguments are enclosed in
|
|
square brackets (``[]``) in the command syntax; the square brackets must not be
|
|
typed. Alternatives in the command syntax are separated by a vertical bar
|
|
(``|``).
|
|
|
|
Entering a blank line repeats the last command entered. Exception: if the last
|
|
command was a :pdbcmd:`list` command, the next 11 lines are listed.
|
|
|
|
Commands that the debugger doesn't recognize are assumed to be Python statements
|
|
and are executed in the context of the program being debugged. Python
|
|
statements can also be prefixed with an exclamation point (``!``). This is a
|
|
powerful way to inspect the program being debugged; it is even possible to
|
|
change a variable or call a function. When an exception occurs in such a
|
|
statement, the exception name is printed but the debugger's state is not
|
|
changed.
|
|
|
|
The debugger supports :ref:`aliases <debugger-aliases>`. Aliases can have
|
|
parameters which allows one a certain level of adaptability to the context under
|
|
examination.
|
|
|
|
Multiple commands may be entered on a single line, separated by ``;;``. (A
|
|
single ``;`` is not used as it is the separator for multiple commands in a line
|
|
that is passed to the Python parser.) No intelligence is applied to separating
|
|
the commands; the input is split at the first ``;;`` pair, even if it is in the
|
|
middle of a quoted string.
|
|
|
|
.. index::
|
|
pair: .pdbrc; file
|
|
triple: debugger; configuration; file
|
|
|
|
If a file :file:`.pdbrc` exists in the user's home directory or in the current
|
|
directory, it is read in and executed as if it had been typed at the debugger
|
|
prompt. This is particularly useful for aliases. If both files exist, the one
|
|
in the home directory is read first and aliases defined there can be overridden
|
|
by the local file.
|
|
|
|
.. versionchanged:: 3.2
|
|
:file:`.pdbrc` can now contain commands that continue debugging, such as
|
|
:pdbcmd:`continue` or :pdbcmd:`next`. Previously, these commands had no
|
|
effect.
|
|
|
|
|
|
.. pdbcommand:: h(elp) [command]
|
|
|
|
Without argument, print the list of available commands. With a *command* as
|
|
argument, print help about that command. ``help pdb`` displays the full
|
|
documentation (the docstring of the :mod:`pdb` module). Since the *command*
|
|
argument must be an identifier, ``help exec`` must be entered to get help on
|
|
the ``!`` command.
|
|
|
|
.. pdbcommand:: w(here)
|
|
|
|
Print a stack trace, with the most recent frame at the bottom. An arrow
|
|
indicates the current frame, which determines the context of most commands.
|
|
|
|
.. pdbcommand:: d(own) [count]
|
|
|
|
Move the current frame *count* (default one) levels down in the stack trace
|
|
(to a newer frame).
|
|
|
|
.. pdbcommand:: u(p) [count]
|
|
|
|
Move the current frame *count* (default one) levels up in the stack trace (to
|
|
an older frame).
|
|
|
|
.. pdbcommand:: b(reak) [([filename:]lineno | function) [, condition]]
|
|
|
|
With a *lineno* argument, set a break there in the current file. With a
|
|
*function* argument, set a break at the first executable statement within
|
|
that function. The line number may be prefixed with a filename and a colon,
|
|
to specify a breakpoint in another file (probably one that hasn't been loaded
|
|
yet). The file is searched on :data:`sys.path`. Note that each breakpoint
|
|
is assigned a number to which all the other breakpoint commands refer.
|
|
|
|
If a second argument is present, it is an expression which must evaluate to
|
|
true before the breakpoint is honored.
|
|
|
|
Without argument, list all breaks, including for each breakpoint, the number
|
|
of times that breakpoint has been hit, the current ignore count, and the
|
|
associated condition if any.
|
|
|
|
.. pdbcommand:: tbreak [([filename:]lineno | function) [, condition]]
|
|
|
|
Temporary breakpoint, which is removed automatically when it is first hit.
|
|
The arguments are the same as for :pdbcmd:`break`.
|
|
|
|
.. pdbcommand:: cl(ear) [filename:lineno | bpnumber ...]
|
|
|
|
With a *filename:lineno* argument, clear all the breakpoints at this line.
|
|
With a space separated list of breakpoint numbers, clear those breakpoints.
|
|
Without argument, clear all breaks (but first ask confirmation).
|
|
|
|
.. pdbcommand:: disable [bpnumber ...]
|
|
|
|
Disable the breakpoints given as a space separated list of breakpoint
|
|
numbers. Disabling a breakpoint means it cannot cause the program to stop
|
|
execution, but unlike clearing a breakpoint, it remains in the list of
|
|
breakpoints and can be (re-)enabled.
|
|
|
|
.. pdbcommand:: enable [bpnumber ...]
|
|
|
|
Enable the breakpoints specified.
|
|
|
|
.. pdbcommand:: ignore bpnumber [count]
|
|
|
|
Set the ignore count for the given breakpoint number. If count is omitted,
|
|
the ignore count is set to 0. A breakpoint becomes active when the ignore
|
|
count is zero. When non-zero, the count is decremented each time the
|
|
breakpoint is reached and the breakpoint is not disabled and any associated
|
|
condition evaluates to true.
|
|
|
|
.. pdbcommand:: condition bpnumber [condition]
|
|
|
|
Set a new *condition* for the breakpoint, an expression which must evaluate
|
|
to true before the breakpoint is honored. If *condition* is absent, any
|
|
existing condition is removed; i.e., the breakpoint is made unconditional.
|
|
|
|
.. pdbcommand:: commands [bpnumber]
|
|
|
|
Specify a list of commands for breakpoint number *bpnumber*. The commands
|
|
themselves appear on the following lines. Type a line containing just
|
|
``end`` to terminate the commands. An example::
|
|
|
|
(Pdb) commands 1
|
|
(com) p some_variable
|
|
(com) end
|
|
(Pdb)
|
|
|
|
To remove all commands from a breakpoint, type ``commands`` and follow it
|
|
immediately with ``end``; that is, give no commands.
|
|
|
|
With no *bpnumber* argument, ``commands`` refers to the last breakpoint set.
|
|
|
|
You can use breakpoint commands to start your program up again. Simply use
|
|
the :pdbcmd:`continue` command, or :pdbcmd:`step`,
|
|
or any other command that resumes execution.
|
|
|
|
Specifying any command resuming execution
|
|
(currently :pdbcmd:`continue`, :pdbcmd:`step`, :pdbcmd:`next`,
|
|
:pdbcmd:`return`, :pdbcmd:`jump`, :pdbcmd:`quit` and their abbreviations)
|
|
terminates the command list (as if
|
|
that command was immediately followed by end). This is because any time you
|
|
resume execution (even with a simple next or step), you may encounter another
|
|
breakpoint—which could have its own command list, leading to ambiguities about
|
|
which list to execute.
|
|
|
|
If you use the 'silent' command in the command list, the usual message about
|
|
stopping at a breakpoint is not printed. This may be desirable for breakpoints
|
|
that are to print a specific message and then continue. If none of the other
|
|
commands print anything, you see no sign that the breakpoint was reached.
|
|
|
|
.. pdbcommand:: s(tep)
|
|
|
|
Execute the current line, stop at the first possible occasion (either in a
|
|
function that is called or on the next line in the current function).
|
|
|
|
.. pdbcommand:: n(ext)
|
|
|
|
Continue execution until the next line in the current function is reached or
|
|
it returns. (The difference between :pdbcmd:`next` and :pdbcmd:`step` is
|
|
that :pdbcmd:`step` stops inside a called function, while :pdbcmd:`next`
|
|
executes called functions at (nearly) full speed, only stopping at the next
|
|
line in the current function.)
|
|
|
|
.. pdbcommand:: unt(il) [lineno]
|
|
|
|
Without argument, continue execution until the line with a number greater
|
|
than the current one is reached.
|
|
|
|
With a line number, continue execution until a line with a number greater or
|
|
equal to that is reached. In both cases, also stop when the current frame
|
|
returns.
|
|
|
|
.. versionchanged:: 3.2
|
|
Allow giving an explicit line number.
|
|
|
|
.. pdbcommand:: r(eturn)
|
|
|
|
Continue execution until the current function returns.
|
|
|
|
.. pdbcommand:: c(ont(inue))
|
|
|
|
Continue execution, only stop when a breakpoint is encountered.
|
|
|
|
.. pdbcommand:: j(ump) lineno
|
|
|
|
Set the next line that will be executed. Only available in the bottom-most
|
|
frame. This lets you jump back and execute code again, or jump forward to
|
|
skip code that you don't want to run.
|
|
|
|
It should be noted that not all jumps are allowed -- for instance it is not
|
|
possible to jump into the middle of a :keyword:`for` loop or out of a
|
|
:keyword:`finally` clause.
|
|
|
|
.. pdbcommand:: l(ist) [first[, last]]
|
|
|
|
List source code for the current file. Without arguments, list 11 lines
|
|
around the current line or continue the previous listing. With ``.`` as
|
|
argument, list 11 lines around the current line. With one argument,
|
|
list 11 lines around at that line. With two arguments, list the given range;
|
|
if the second argument is less than the first, it is interpreted as a count.
|
|
|
|
The current line in the current frame is indicated by ``->``. If an
|
|
exception is being debugged, the line where the exception was originally
|
|
raised or propagated is indicated by ``>>``, if it differs from the current
|
|
line.
|
|
|
|
.. versionadded:: 3.2
|
|
The ``>>`` marker.
|
|
|
|
.. pdbcommand:: ll | longlist
|
|
|
|
List all source code for the current function or frame. Interesting lines
|
|
are marked as for :pdbcmd:`list`.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. pdbcommand:: a(rgs)
|
|
|
|
Print the argument list of the current function.
|
|
|
|
.. pdbcommand:: p expression
|
|
|
|
Evaluate the *expression* in the current context and print its value.
|
|
|
|
.. note::
|
|
|
|
``print()`` can also be used, but is not a debugger command --- this executes the
|
|
Python :func:`print` function.
|
|
|
|
|
|
.. pdbcommand:: pp expression
|
|
|
|
Like the :pdbcmd:`p` command, except the value of the expression is
|
|
pretty-printed using the :mod:`pprint` module.
|
|
|
|
.. pdbcommand:: whatis expression
|
|
|
|
Print the type of the *expression*.
|
|
|
|
.. pdbcommand:: source expression
|
|
|
|
Try to get source code for the given object and display it.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. pdbcommand:: display [expression]
|
|
|
|
Display the value of the expression if it changed, each time execution stops
|
|
in the current frame.
|
|
|
|
Without expression, list all display expressions for the current frame.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. pdbcommand:: undisplay [expression]
|
|
|
|
Do not display the expression any more in the current frame. Without
|
|
expression, clear all display expressions for the current frame.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. pdbcommand:: interact
|
|
|
|
Start an interactive interpreter (using the :mod:`code` module) whose global
|
|
namespace contains all the (global and local) names found in the current
|
|
scope.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. _debugger-aliases:
|
|
|
|
.. pdbcommand:: alias [name [command]]
|
|
|
|
Create an alias called *name* that executes *command*. The command must
|
|
*not* be enclosed in quotes. Replaceable parameters can be indicated by
|
|
``%1``, ``%2``, and so on, while ``%*`` is replaced by all the parameters.
|
|
If no command is given, the current alias for *name* is shown. If no
|
|
arguments are given, all aliases are listed.
|
|
|
|
Aliases may be nested and can contain anything that can be legally typed at
|
|
the pdb prompt. Note that internal pdb commands *can* be overridden by
|
|
aliases. Such a command is then hidden until the alias is removed. Aliasing
|
|
is recursively applied to the first word of the command line; all other words
|
|
in the line are left alone.
|
|
|
|
As an example, here are two useful aliases (especially when placed in the
|
|
:file:`.pdbrc` file)::
|
|
|
|
# Print instance variables (usage "pi classInst")
|
|
alias pi for k in %1.__dict__.keys(): print("%1.",k,"=",%1.__dict__[k])
|
|
# Print instance variables in self
|
|
alias ps pi self
|
|
|
|
.. pdbcommand:: unalias name
|
|
|
|
Delete the specified alias.
|
|
|
|
.. pdbcommand:: ! statement
|
|
|
|
Execute the (one-line) *statement* in the context of the current stack frame.
|
|
The exclamation point can be omitted unless the first word of the statement
|
|
resembles a debugger command. To set a global variable, you can prefix the
|
|
assignment command with a :keyword:`global` statement on the same line,
|
|
e.g.::
|
|
|
|
(Pdb) global list_options; list_options = ['-l']
|
|
(Pdb)
|
|
|
|
.. pdbcommand:: run [args ...]
|
|
restart [args ...]
|
|
|
|
Restart the debugged Python program. If an argument is supplied, it is split
|
|
with :mod:`shlex` and the result is used as the new :data:`sys.argv`.
|
|
History, breakpoints, actions and debugger options are preserved.
|
|
:pdbcmd:`restart` is an alias for :pdbcmd:`run`.
|
|
|
|
.. pdbcommand:: q(uit)
|
|
|
|
Quit from the debugger. The program being executed is aborted.
|
|
|
|
.. pdbcommand:: debug code
|
|
|
|
Enter a recursive debugger that steps through the code
|
|
argument (which is an arbitrary expression or statement to be
|
|
executed in the current environment).
|
|
|
|
.. pdbcommand:: retval
|
|
|
|
Print the return value for the last return of a function.
|
|
|
|
.. rubric:: Footnotes
|
|
|
|
.. [1] Whether a frame is considered to originate in a certain module
|
|
is determined by the ``__name__`` in the frame globals.
|