Doc/library/trace.rst

:mod:`trace` --- Trace or track Python statement execution
==========================================================

.. module:: trace
   :synopsis: Trace or track Python statement execution.


The :mod:`trace` module allows you to trace program execution, generate
annotated statement coverage listings, print caller/callee relationships and
list functions executed during a program run.  It can be used in another program
or from the command line.

.. seealso::

   Latest version of the :source:`trace module Python source code
   <Lib/trace.py>`

.. _trace-cli:

Command-Line Usage
------------------

The :mod:`trace` module can be invoked from the command line.  It can be as
simple as ::

   python -m trace --count -C . somefile.py ...

The above will execute :file:`somefile.py` and generate annotated listings of all
Python modules imported during the execution into the current directory.

.. program:: trace

.. cmdoption:: --help

   Display usage and exit.

.. cmdoption:: --version

   Display the version of the module and exit.

Main options
^^^^^^^^^^^^

At least one of the following options must be specified when invoking :mod:`trace`.
The :option:`--listfuncs <-l>` option is mutually exclusive with the
:option:`--trace <-t>` and :option:`--counts <-c>` options . When :option:`--listfuncs <-l>`
is provided, neither :option:`--counts <-c>` nor :option:`--trace <-t>` are accepted,
and vice versa.

.. program:: trace

.. cmdoption:: -c, --count

   Produce a set of annotated listing files upon program completion that shows
   how many times each statement was executed.
   See also :option:`--coverdir <-C>`, :option:`--file <-f>`,
   :option:`--no-report <-R>` below.

.. cmdoption:: -t, --trace

   Display lines as they are executed.

.. cmdoption:: -l, --listfuncs

   Display the functions executed by running the program.

.. cmdoption:: -r, --report

   Produce an annotated list from an earlier program run that used the
   :option:`--count <-c>` and :option:`--file <-f>` option. Do not execute any code.

.. cmdoption:: -T, --trackcalls

   Display the calling relationships exposed by running the program.

Modifiers
^^^^^^^^^

.. program:: trace

.. cmdoption:: -f, --file=<file>

   Name of a file to accumulate counts over several tracing runs. Should be used
   with the :option:`--count <-c>` option.

.. cmdoption:: -C, --coverdir=<dir>

   Directory where the report files go. The coverage report for
   ``package.module`` is written to file :file:`{dir}/{package}/{module}.cover`.

.. cmdoption:: -m, --missing

   When generating annotated listings, mark lines which were not executed with
   ``>>>>>>``.

.. cmdoption:: -s, --summary

   When using :option:`--count <-c>` or :option:`--report <-r>`, write a brief
   summary to stdout for each file processed.

.. cmdoption:: -R, --no-report

   Do not generate annotated listings.  This is useful if you intend to make
   several runs with :option:`--count <-c>`, and then produce a single set of
   annotated listings at the end.

.. cmdoption:: -g, --timing

   Prefix each line with the time since the program started. Only used while
   tracing.

Filters
^^^^^^^

These options may be repeated multiple times.

.. program:: trace

.. cmdoption:: --ignore-module=<mod>

   Ignore each of the given module names and its submodules (if it is a package).
   The argument can be a list of names separated by a comma.

.. cmdoption:: --ignore-dir=<dir>

   Ignore all modules and packages in the named directory and subdirectories.
   The argument can be a list of directories separated by :data:`os.pathsep`.

.. _trace-api:

Programmatic Interface
----------------------

.. class:: Trace(count=1, trace=1, countfuncs=0, countcallers=0, ignoremods=(), ignoredirs=(), infile=None, outfile=None, timing=False)

   Create an object to trace execution of a single statement or expression. All
   parameters are optional.  *count* enables counting of line numbers. *trace*
   enables line execution tracing.  *countfuncs* enables listing of the functions
   called during the run.  *countcallers* enables call relationship tracking.
   *ignoremods* is a list of modules or packages to ignore.  *ignoredirs* is a list
   of directories whose modules or packages should be ignored.  *infile* is the
   name of the file from which to read stored count information.  *outfile* is
   the name of the file in which to write updated count information. *timing*
   enables a timestamp relative to when tracing was started to be displayed.

.. method:: Trace.run(cmd)

   Execute the command and gather statistics from the execution with
   the current tracing parameters.
   *cmd* must be a string or code object, suitable for passing into :func:`exec`.

.. method:: Trace.runctx(cmd, globals=None, locals=None)

   Execute the command and gather statistics from the execution with
   the current tracing parameters, in the defined global and local environments.
   If not defined, *globals* and *locals* default to empty dictionaries.

.. method:: Trace.runfunc(func, *args, **kwds)

   Call *func* with the given arguments under control of the :class:`Trace` object
   with the current tracing parameters.

.. method:: Trace.results()

   Return a :class:`CoverageResults` object that contains the cumulative results
   of all previous calls to ``run``, ``runctx`` and ``runfunc`` for the given
   :class:`Trace` instance. Does not reset the accumulated trace results.

.. class:: CoverageResults

   A container for coverage results, created by :meth:`Trace.results`. Should not
   be created directly by the user.

.. method:: CoverageResults.update(other)

   Merge in data from another :class:`CoverageResults` object.

.. method:: CoverageResults.write_results(show_missing=True, summary=False, coverdir=None)

   Write coverage results. Set *show_missing* to show lines that had no hits.
   Set *summary* to include in the output the coverage summary per module. *coverdir*
   specifies the directory into which the coverage result files will be output.
   If ``None``, the results for each source file are placed in its directory.

A simple example demonstrating the use of the programmatic interface::

   import sys
   import trace

   # create a Trace object, telling it what to ignore, and whether to
   # do tracing or line-counting or both.
   tracer = trace.Trace(
       ignoredirs=[sys.prefix, sys.exec_prefix],
       trace=0,
       count=1)

   # run the new command using the given tracer
   tracer.run('main()')

   # make a report, placing output in /tmp
   r = tracer.results()
   r.write_results(show_missing=True, coverdir="/tmp")