>>> def foo(bar, *args, **kwargs):
pass
>>> foo('a', bar='b')
TypeError: foo() got multiple values for keyword argument 'bar'
>>> def foo(*, bar):
pass
>>> def foo(bar, *args, **kwargs):
pass
>>> foo('a', bar='b')
TypeError: foo() got multiple values for keyword argument 'bar'
>>> def foo(*, bar):
pass
*** Python 3.0 (r30:67507, Dec 3 2008, 20:14:27) [MSC v.1500 32 bit (Intel)] on win32. ***
>>> filter
<class 'filter'>