Checking for invalid keyword arguments?

[Roy Smith]

I've got a function that takes a couple of optional keyword arguments.  
I want to check to make sure I didn't get passed an argument I didn't 
expect.  Right now I'm doing:

        conversion = None
        drop = False
        for key, value in kwArgs.items():
            if key == 'conversion':
                conversion = value
            elif key == 'drop':
                drop = value
            else:
                raise TypeError ('Unexpected keyword argument %s' % key)

which seems kind of verbose.  Is there a neater way to do this check?