: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.

.. _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 somefile.py ...

The above will generate annotated listings of all Python modules imported during

the execution of :file:`somefile.py`.

The following command-line arguments are supported:

:option:`--trace`, :option:`-t`

   Display lines as they are executed.

:option:`--count`, :option:`-c`

   Produce a set of  annotated listing files upon program completion that shows how

   many times each statement was executed.

:option:`--report`, :option:`-r`

   Produce an annotated list from an earlier program run that used the

   :option:`--count` and :option:`--file` arguments.

:option:`--no-report`, :option:`-R`

   Do not generate annotated listings.  This is useful if you intend to make

   several runs with :option:`--count` then produce a single set of annotated

   listings at the end.

:option:`--listfuncs`, :option:`-l`

   List the functions executed by running the program.

:option:`--trackcalls`, :option:`-T`

   Generate calling relationships exposed by running the program.

:option:`--file`, :option:`-f`

   Name a file containing (or to contain) counts.

:option:`--coverdir`, :option:`-C`

   Name a directory in which to save annotated listing files.

:option:`--missing`, :option:`-m`

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

   '``>>>>>>``'.

:option:`--summary`, :option:`-s`

   When using :option:`--count` or :option:`--report`, write a brief summary to

   stdout for each file processed.

:option:`--ignore-module`

   Accepts comma separated list of module names. Ignore each of the named

   module and its submodules (if it is a package).  May be given 

   multiple times.

:option:`--ignore-dir`

   Ignore all modules and packages in the named directory and subdirectories

   (multiple directories can be joined by os.pathsep).  May be given multiple

   times. 

.. _trace-api:

Programming 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

   file from which to read stored count information.  *outfile* is a 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)

   Run *cmd* under control of the Trace object with the current tracing parameters.

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

   Run *cmd* under control of the Trace object 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.

This is a simple example showing the use of this module::

   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")