Import a module from a relative path

How do I import a Python module given its relative path?

For example, if dirFoo contains Foo.py and dirBar, and dirBar contains Bar.py, how do I import Bar.py into Foo.py?

Here's a visual representation:

dirFoo\
    Foo.py
    dirBar\
        Bar.py

Foo wishes to include Bar, but restructuring the folder hierarchy is not an option.