[Python-3000] PEP3102 Keyword-Only Arguments (original) (raw)

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 arguments.

STeVe

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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