Watching which function is called in Python

Question

What is the easiest way to record function calls for debugging in Python? I'm usually interested in particular functions or all functions from a given class. Or sometimes even all functions called on a particular object attribute. Seeing the call arguments would be useful, too.

I can imagine writing decorators for all that, but then I'd still have to modify the source code in different places. And writing a class decorator which modifies all methods isn't that straightforward.

Is there a solution where I don't have to modify my source code? Ideally something which doesn't slow down Python too much.

You could monkey patch object itself when in 'debug mode' and reconfigure __getattribute__, __setattr__, and maybe __call__, then use some sort of filtering mechanism to define which things you want to log and which not. Though @StevenRumbalski's question deserves answering first. — Silas Ray
– Silas Ray, Commented Nov 27, 2012 at 15:41
Possible duplicate of stackoverflow.com/questions/582336/…, if you're interested in call counts, etc. — aquavitae
– aquavitae, Commented Nov 27, 2012 at 15:42
@Steven: I only know normal pdb usage. But I'd rather have a full program run and just a report of function calls. Is there a good solution with the debugging tools? — Gere
– Gere, Commented Nov 27, 2012 at 15:46

martineau · Accepted Answer · 2012-12-01 21:18:00Z

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You ought to be able to implement something that does what you want using either sys.setprofile() or perhaps sys.settrace(). They both let you define a function to be called when specific "events" occur, like function calls, and pass additional information to which can be used to to determine the function/method being called and examine its arguments.

If you look around, there's probably sample usage code to use as a good starting point.

edited Dec 1, 2012 at 21:18

answered Nov 27, 2012 at 18:54

martineau

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moonsly · Accepted Answer · 2012-11-27 17:44:08Z

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Except decorators, for Python >= 3.0 you could use new __getattribute__ method for a class, which will be called every time you call any method of the object. You could look through Lutz "Learning Python" chapters 31, 37 about it.

answered Nov 27, 2012 at 17:44

moonsly

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martineau Over a year ago

__getattribute__ exists in Python 2, too, as part of new-style classes introduced in Python 2.2. Not sure what you meant by "Except decorators"...

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