How to - import code not in current directory

[py]

I have a python script that I want to test/debug.  It contains a class
which extends from some other class which is located in some other
python file in a different directory.

For example:

[script to test]
c:\python_code\foo.py

[needed python files]
c:\some\other\directory\bar.py

...so I want to test/debug foo.py, which needs bar.py.  foo.py imports
bar.py ...but in order to test out foo (in the python shell) I normally
copy bar.py into the same directory as foo.py...but this is painful.
Is there some way that I can have python know about the directory where
bar.py is located, like a system variable, etc?  If so, how do I set
that up?

Thanks.