\section{\module{trace} ---
         Trace or track Python statement execution}

\declaremodule{standard}{trace}
\modulesynopsis{Trace or track Python statement execution.}

The \module{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.

\subsection{Command Line Usage}

The \module{trace} module can be invoked from the command line.  It can be
as simple as

\begin{verbatim}
python -m trace --count somefile.py ...
\end{verbatim}

The above will generate annotated listings of all Python modules imported
during the execution of \code{somefile.py}.

\subsection{Command Line Arguments}

\begin{description}
\item[--trace, -t]{Display lines as they are executed.}
\item[--count, -c]{Produce a set of  annotated listing files upon program
completion that shows how many times each statement was executed.}
\item[--report, -r]{Produce an annotated list from an earlier program run that
used the \code{--count} and \code{--file} arguments.}
\item[--no-report, -R]{Do not generate annotated listings.  This is useful
if you intend to make several runs with \code{--count} then produce a single
set of annotated listings at the end.}
\item[--listfuncs, -l]{List the functions executed by running the program.}
\item[--trackcalls, -T]{Generate calling relationships exposed by running the
program.}
\item[--file, -f]{Name a file containing (or to contain) counts.}
\item[--coverdir, -C]{Name a directory in which to save annotated listing
files.}
\item[--missing, -m]{When generating annotated listings, mark lines which
were not executed with \code{>>>>>>}.}
\item[--summary -s]{When using \code{--count} or \code{--report}, write a
brief summary to stdout for each file processed.}
\item[--ignore-module]{Ignore the named module and its submodules (if it is
a package).  May be given multiple times.}
\item[--ignore-dir]{Ignore all modules and packages in the named directory
and subdirectories.  May be given multiple times.}
\end{description}

\subsection{Program Usage}

\begin{classdesc}{Trace}{\optional{count=1\optional{,trace=1\optional{,countfuncs=0\optional{,countcallers=0\optional{,ignoremods=()\optional{,ignoredirs=()\optional{,infile=None\optional{,outfile=None}}}}}}}}}

Create an object to trace execution of a single statement or expression.
All parameters are optional.  \var{count} enables counting of line numbers.
\var{trace} enables line execution tracing.  \var{countfuncs} enables
listing of the functions called during the run.  \var{countcallers} enables
call relationship tracking.  \var{ignoremods} is a list of modules or
packages to ignore.  \var{ignoredirs} is a list of directories whose modules
or packages should be ignored.  \var{infile} is the file from which to read
stored count information.  \var{outfile} is a file in which to write updated
count information.

\end{classdesc}

\begin{methoddesc}[Trace]{run}{cmd}
Run \code{cmd} under control of the Trace object with the current tracing
parameters.
\end{methoddesc}

\begin{methoddesc}[Trace]{runctx}{cmd\optional{,globals=None\optional{,locals=None}}}
Run \code{cmd} under control of the Trace object with the current tracing
parameters in the defined global and local environments.  If not defined,
\code{globals} and \code{locals} default to empty dictionaries.
\end{methoddesc}

\begin{methoddesc}[Trace]{runfunc}{func, *args, **kwds}
Call \code{function} with the given arguments under control of the Trace
object with the current tracing parameters.
\end{methoddesc}

\subsubsection{Example}

\begin{verbatim}
import sys

# 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")
\end{verbatim}