Functions with positional only arguments

This came from a discussion on the python-ideas mailing list. The file posonly.py(download here) defines a function posonly that can be used to decorate functions so that their arguments become positional only (i.e. they can't be given as keywords). Below are a few examples of how this can be used.

Here are some examples of use:

>>> @posonly
... def f(x, y=1): return x, y
... 
>>> f(1)
(1, 1)
>>> f(1, y=2)
Traceback (most recent call last):
  File "", line 1, in ?
TypeError: f() got an unexpected keyword argument 'y'
>>> f(x=1)
Traceback (most recent call last):
  File "", line 1, in ?
TypeError: f() got an unexpected keyword argument 'x'
>>> @posonly
... def update(self, container=None, **kwargs):
...     "Pretend function"
...     return self, container, kwargs
... 
>>> # self and container can be used as keyword argument names
... update('self', 'container', self=1, container=2)
('self', 'container', {'self': 1, 'container': 2})
>>> # There is still a way to access posonly args by name...
... f(**{'x@':'spam'})
('spam', 1)
>>> # @posonly preserves __doc__ and __name__
... # Positional only arguments are followed by a '@'
... help(update)
Help on function update in module __main__:

update(self@, container@, **kwargs)
    Pretend function
>>>