[yummyfajitas]

I wasn't actually trying to make a statement about type systems. To translate my example to python:

    def getFileHandleOrNone(filename, config):
        ...

    def foo(filename, config):
        """get file handle or none, 
           based on context and filesystem"""

You are correct that the type system also provides documentation, but so does giving your methods a name indicating what you want them to do.