[Python-3000] PEP3102 Keyword-Only Arguments

Steven Bethard steven.bethard at gmail.com
Mon Aug 14 19:49:36 CEST 2006

On 8/14/06, Guido van Rossum <guido at python.org> wrote:
> I believe the PEP doesn't address the opposite use case: positional
> arguments that should *not* be specified as keyword arguments. For
> example, I might want to write
>   def foo(a, b): ...
> but I don't want callers to be able to call it as foo(b=1, a=2) or
> even foo(a=2, b=1).

Another use case is when you want to accept the arguments of another
callable, but you have your own positional arguments::

    >>> class Wrapper(object):
    ...     def __init__(self, func):
    ...         self.func = func
    ...     def __call__(self, *args, **kwargs):
    ...         print 'calling wrapped function'
    ...         return self.func(*args, **kwargs)
    >>> @Wrapper
    ... def func(self, other):
    ...     return self, other
    >>> func(other=1, self=2)
    Traceback (most recent call last):
      File "<interactive input>", line 1, in ?
    TypeError: __call__() got multiple values for keyword argument 'self'

It would be really nice in the example above to mark ``self`` in
``__call__`` as a positional only argument.

> Perhaps we can use ** without following identifier to signal this?
> It's not entirely analogous to * without following identifier, but at
> least somewhat similar.

I'm certainly not opposed to going this way, but I don't think it
would solve the problem above since you still need to take keyword

I'm not *in*-sane. Indeed, I am so far *out* of sane that you appear a
tiny blip on the distant coast of sanity.
        --- Bucky Katt, Get Fuzzy

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