:mod:`!trace` --- Trace or track Python statement execution
===========================================================
.. module:: trace
:synopsis: Trace or track Python statement execution.
**Source code:** :source:`Lib/trace.py`
--------------
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::
`Coverage.py <https://coverage.readthedocs.io/>`_
A popular third-party coverage tool that provides HTML
output along with advanced features such as branch coverage.
.. _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
.. option:: --help
Display usage and exit.
.. option:: --version
Display the version of the module and exit.
.. versionadded:: 3.8
Added ``--module`` option that allows to run an executable module.
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:`--count <-c>` options. When
:option:`--listfuncs <-l>` is provided, neither :option:`--count <-c>` nor
:option:`--trace <-t>` are accepted, and vice versa.
.. program:: trace
.. option:: -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>` and
:option:`--no-report <-R>` below.
.. option:: -t, --trace
Display lines as they are executed.
.. option:: -l, --listfuncs
Display the functions executed by running the program.
.. option:: -r, --report
Produce an annotated list from an earlier program run that used the
:option:`--count <-c>` and :option:`--file <-f>` option. This does not
execute any code.
.. option:: -T, --trackcalls
Display the calling relationships exposed by running the program.
Modifiers
^^^^^^^^^
.. program:: trace
.. option:: -f, --file=<file>
Name of a file to accumulate counts over several tracing runs. Should be
used with the :option:`--count <-c>` option.
.. option:: -C, --coverdir=<dir>
Directory where the report files go. The coverage report for
``package.module`` is written to file :file:`{dir}/{package}/{module}.cover`.
.. option:: -m, --missing
When generating annotated listings, mark lines which were not executed with
``>>>>>>``.
.. option:: -s, --summary
When using :option:`--count <-c>` or :option:`--report <-r>`, write a brief
summary to stdout for each file processed.
.. option:: -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.
.. option:: -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
.. option:: --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.
.. option:: --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:: 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:: 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:: runfunc(func, /, *args, **kwds)
Call *func* with the given arguments under control of the :class:`Trace`
object with the current tracing parameters.
.. method:: 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:: update(other)
Merge in data from another :class:`CoverageResults` object.
.. method:: write_results(show_missing=True, summary=False, coverdir=None,\
*, ignore_missing_files=False)
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.
If *ignore_missing_files* is ``True``, coverage counts for files that no
longer exist are silently ignored. Otherwise, a missing file will
raise a :exc:`FileNotFoundError`.
.. versionchanged:: 3.13
Added *ignore_missing_files* parameter.
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 the current directory
r = tracer.results()
r.write_results(show_missing=True, coverdir=".")
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