Find out where a class is used throughout a program.

[Azureaus]

Hi All,
I'm fairly new to Python so please forgive me If I sound confused or include anything a bit irrelevant. I've had some great responses from this group already though so thanks.

I have a source file that is laid out roughly like

class:
class methods
methods 
init statement
class:
method

It doesn't seem to have a run method unlike other similar source files I have so it seems to be that this is being referenced from other files and is almost a 'utility file'.

To try and make this question as general as possible - is there a way of finding out / visualising where a particular class is called/used throughout a program? I need to find out the way in which these classes are being used and their typical input (and where the output from these are going) so I can have a play around and really figure out how it works. Without a run method to call, or an idea of expected input/output it's difficult. Also without some sort of trace it's difficult.

I spoke to colleague and was told to look into dir() method in a Python shell which I will do this evening but if anyone has any suggestions that would be great. Even better if you think this is what I'm after a quick example/use case would be even better. Or maybe I'm looking at this the wrong way and you can point me towards some docs?
Thanks for your help.