26.5. 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.

26.5.1. Command Line Usage

The 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 somefile.py.

The following command-line arguments are supported:

--trace, -t

Display lines as they are executed.

--count, -c

Produce a set of annotated listing files upon program completion that shows how many times each statement was executed.

--report, -r

Produce an annotated list from an earlier program run that used the --count and --file arguments.

--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.

--listfuncs, -l

List the functions executed by running the program.

--trackcalls, -T

Generate calling relationships exposed by running the program.

--file, -f

Name a file containing (or to contain) counts.

--coverdir, -C

Name a directory in which to save annotated listing files.

--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.

--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.

--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.

26.5.2. Programming Interface

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 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.

Trace.run(cmd)

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

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.

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")