How do I profile a Python script?

Python includes a profiler called cProfile. It not only gives the total running time, but also times each function separately, and tells you how many times each function was called, making it easy to determine where you should make optimizations.

You can call it from within your code, or from the interpreter, like this:

import cProfile
cProfile.run('foo()')

Even more usefully, you can invoke cProfile when running a script:

python -m cProfile myscript.py

Or when running a module:

python -m cProfile -m mymodule

To make it even easier, I made a little batch file called 'profile.bat':

python -m cProfile %1

So all I have to do is run:

profile euler048.py

And I get this:

1007 function calls in 0.061 CPU seconds

Ordered by: standard name
ncalls  tottime  percall  cumtime  percall filename:lineno(function)
    1    0.000    0.000    0.061    0.061 <string>:1(<module>)
 1000    0.051    0.000    0.051    0.000 euler048.py:2(<lambda>)
    1    0.005    0.005    0.061    0.061 euler048.py:2(<module>)
    1    0.000    0.000    0.061    0.061 {execfile}
    1    0.002    0.002    0.053    0.053 {map}
    1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler objects}
    1    0.000    0.000    0.000    0.000 {range}
    1    0.003    0.003    0.003    0.003 {sum}

For more information, check out this tutorial from PyCon 2013 titled Python Profiling
Also via YouTube.

A while ago I made pycallgraph which generates a visualisation from your Python code. Edit: I've updated the example to work with 3.3, the latest release as of this writing.

After a pip install pycallgraph and installing GraphViz you can run it from the command line:

pycallgraph graphviz -- ./mypythonscript.py

Or, you can profile particular parts of your code:

from pycallgraph import PyCallGraph
from pycallgraph.output import GraphvizOutput

with PyCallGraph(output=GraphvizOutput()):
    code_to_profile()

Either of these will generate a pycallgraph.png file similar to the image below:

It's worth pointing out that using the profiler only works (by default) on the main thread, and you won't get any information from other threads if you use them. This can be a bit of a gotcha as it is completely unmentioned in the profiler documentation.

If you also want to profile threads, you'll want to look at the threading.setprofile() function in the docs.

You could also create your own threading.Thread subclass to do it:

class ProfiledThread(threading.Thread):
    # Overrides threading.Thread.run()
    def run(self):
        profiler = cProfile.Profile()
        try:
            return profiler.runcall(threading.Thread.run, self)
        finally:
            profiler.dump_stats('myprofile-%d.profile' % (self.ident,))

and use that ProfiledThread class instead of the standard one. It might give you more flexibility, but I'm not sure it's worth it, especially if you are using third-party code which wouldn't use your class.

The python wiki is a great page for profiling resources: http://wiki.python.org/moin/PythonSpeed/PerformanceTips#Profiling_Code

as is the python docs: http://docs.python.org/library/profile.html

as shown by Chris Lawlor cProfile is a great tool and can easily be used to print to the screen:

python -m cProfile -s time mine.py <args>

or to file:

python -m cProfile -o output.file mine.py <args>

PS> If you are using Ubuntu, make sure to install python-profile

apt-get install python-profiler 

If you output to file you can get nice visualizations using the following tools

PyCallGraph : a tool to create call graph images
install:

 pip install pycallgraph

run:

 pycallgraph mine.py args

view:

 gimp pycallgraph.png

You can use whatever you like to view the png file, I used gimp
Unfortunately I often get

dot: graph is too large for cairo-renderer bitmaps. Scaling by 0.257079 to fit

which makes my images unusably small. So I generally create svg files:

pycallgraph -f svg -o pycallgraph.svg mine.py <args>

PS> make sure to install graphviz (which provides the dot program):

pip install graphviz

Alternative Graphing using gprof2dot via @maxy / @quodlibetor :

pip install gprof2dot
python -m cProfile -o profile.pstats mine.py
gprof2dot -f pstats profile.pstats | dot -Tsvg -o mine.svg