Help with 'self' and 'set_usage'

[L O'Shea]

Hi all,
I'm interning and have been given the job of extending a program that has been written by someone else. I've never used Python before so it's a bit of a struggle but I've got to say I'm loving the language so far.

In on of the scripts there is

def set_usage(self,s):
self.usage_str = s

Could anyone shed some light on this? I can't find mention of this anywhere in any Python documentation or anywhere else in the code where usage_str might be defined. Can you just create variables in that object by writing self.name = "david" self.hobby = "fishing"??

If this is any help it is used later in the program (or in other scripts) like

prog.set_usage("""%prog <command> [options] ....""")

Thanks for your help, I have spent a good while googling python docs, code snippets and reading through a Python book I have on my desk to no avail.

Cheers in advance.