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<H1><A NAME="SECTION0012800000000000000000">
10.8 Extensions -- Deriving Better Profilers</A>
</H1>
<A NAME="Profiler_Extensions"></A>
<P>
The <tt class="class">Profile</tt> class of module <tt class="module">profile</tt> was written so that
derived classes could be developed to extend the profiler.  The details
are not described here, as doing this successfully requires an expert
understanding of how the <tt class="class">Profile</tt> class works internally.  Study
the source code of module <tt class="module">profile</tt> carefully if you want to
pursue this.

<P>
If all you want to do is change how current time is determined (for
example, to force use of wall-clock time or elapsed process time),
pass the timing function you want to the <tt class="class">Profile</tt> class
constructor:

<P>
<div class="verbatim"><pre>
pr = profile.Profile(your_time_func)
</pre></div>

<P>
The resulting profiler will then call <code>your_time_func()</code>.
The function should return a single number, or a list of
numbers whose sum is the current time (like what <tt class="function">os.times()</tt>
returns).  If the function returns a single time number, or the list of
returned numbers has length 2, then you will get an especially fast
version of the dispatch routine.

<P>
Be warned that you should calibrate the profiler class for the
timer function that you choose.  For most machines, a timer that
returns a lone integer value will provide the best results in terms of
low overhead during profiling.  (<tt class="function">os.times()</tt> is
<em>pretty</em> bad, as it returns a tuple of floating point values).  If
you want to substitute a better timer in the cleanest fashion,
derive a class and hardwire a replacement dispatch method that best
handles your timer call, along with the appropriate calibration
constant.

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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