
``trace`` --- Trace or track Python statement execution
*******************************************************

The ``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.


Command Line Usage
==================

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


Meta-options
------------

``--help``

   Display usage and exit.

``--version``

   Display the version of the module and exit.


Main options
------------

The ``--listfuncs`` option is mutually exclusive with the ``--trace``
and ``--count`` options . When ``--listfuncs`` is provided, neither
``--counts`` nor ``--trace`` are accepted, and vice versa.

``--count, -c``

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

``--trace, -t``

   Display lines as they are executed.

``--listfuncs, -l``

   Display the functions executed by running the program.

``--report, -r``

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

``--trackcalls, -T``

   Display the calling relationships exposed by running the program.


Modifiers
---------

``--file=<file>, -f``

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

``--coverdir=<dir>, -C``

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

``--missing, -m``

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

``--summary, -s``

   When using ``--count`` or ``--report``, write a brief summary to
   stdout for each file processed.

``--no-report, -R``

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

``--timing, -g``

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


Filters
-------

These options may be repeated multiple times.

``--ignore-module=<mod>``

   Accepts comma separated list of module names. Ignore each of the
   named modules and its submodules (if it is a package).

``--ignore-dir=<dir>``

   Ignore all modules and packages in the named directory and
   subdirectories (multiple directories can be joined by
   ``os.pathsep``).


Programming Interface
=====================

class class trace.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.

Trace.run(cmd)

   Run *cmd* under control of the ``Trace`` object with the current
   tracing parameters. *cmd* must be a string or code object, suitable
   for passing into ``exec()``.

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.

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

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

Trace.results()

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

class class trace.CoverageResults

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

CoverageResults.update(other)

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

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 programming 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")
