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<title>'cProfile': the lsprof profiler</title>
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<div class="document" id="cprofile-the-lsprof-profiler">
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<h1 class="title">'cProfile': the lsprof profiler</h1>
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<p>This svn repository directory contains 'cProfile', a C replacement for
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the standard 'profile' module. It should work with any not-too-old
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version of Python. It is now included in the standard library of Python
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<p>Therefore, the situation of the profilers in Python is as follows:</p>
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<p>'profile.Profile' is the ages-old pure Python profiler. At the end of a
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run, it builds a dict that is inspected by 'pstats.Stats'. It has some
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recent support for profiling C calls, which however make it crash in
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some cases <a class="reference" href="https://sourceforge.net/tracker/?group_id=5470&atid=105470&func=detail&aid=1117670">[1]</a>. And of course it's slow (makes a run take about 10x
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<p>'hotshot', new from 2.2, is quite faster (reportedly, only 30% added
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overhead). The log file is then loaded and turned into an instance of
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the same 'pstats.Stats'. This loading takes ages. The reason is that
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the log file only records events, and loading is done by instantiating a
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'profile.Profile' and sending it all the events. In other words, it
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takes exactly as long as the time it saved in the first place!
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Moreover, for some reasons, the results given by hotshot seem sometimes
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quite wrong. (I don't understand why, but I've seen it myself, and it's
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been reported by various people, e.g. <a class="reference" href="http://sourceforge.net/tracker/?group_id=5470&atid=305470&func=detail&aid=1212837">[2]</a>.) 'hotshot' doesn't know
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about C calls, but it can log line events, although this information is
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lost(!) in the final conversion to a 'pstats.Stats'.</p>
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<p>'lsprof' is a third profiler by Brett Rosen and Ted Czotter, posted on
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SF in June 2005 <a class="reference" href="http://sourceforge.net/tracker/?group_id=5470&atid=305470&func=detail&aid=1212837">[2]</a>. Michael Hudson and I did some minor clean-ups and
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improvements on it, and it seems to be quite useful. It is, for
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example, the only of the three profilers that managed to give sensible
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information about the PyPy translation process without crashing,
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allowing us to accelerate it from over 30 to under 20 minutes. The SF
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patch contains a more detailed account on the reasons for writing
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'lsprof'. The current version <a class="reference" href="http://codespeak.net/svn/user/arigo/hack/misc/lsprof">[3]</a> supports C calls but not line events.
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It has its own simple internal interface, which is wrapped in an
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interface compatible with 'profile' by a module called 'cProfile'.
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However, unlike the other two profilers, it can record detailed stats
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about children, which I found quite useful (e.g. how much time is spent
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in a function when it is called by another specific function).</p>
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<p>'lsprof' has been added to the standard library of Python 2.5. Its
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public interface is in 'cProfile', which is designed to be a drop-in
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replacement for 'profile'. The 'pstats' module has also been extended
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in 2.5 to show the extra children statistics recorded by 'cProfile', if
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present. In the stand-alone version of lsprof/cProfile that you can
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download from <a class="reference" href="http://codespeak.net/svn/user/arigo/hack/misc/lsprof">[3]</a>, the extended pstats module is called 'pstats2' to
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avoid collision with the standard 'pstats'. The easiest way to read the
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documentation of cProfile is by looking at the Python 2.5 documentation
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<a class="reference" href="http://www.python.org/doc/2.5/lib/module-profile.html">[4]</a>.</p>
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