cpython/Doc/library/trace.rst

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: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 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")