[Python-ideas] 'Injecting' objects as function-local constants

Wed Jun 15 08:21:47 CEST 2011

On 2011年06月15日 02:28, Jan Kaliszewski wrote:
> Jan Kaliszewski dixit (2011年06月14日, 12:17):
>> But in case of:
>>>> def sth(*args, **kwargs, my_var='foo'): "do something"
>>>> -- should 'my_var' in kwargs be allowed? (it's a runtime question)
>> There is no real conflict here, so at the first sight I'd say: yes. 
>> On second thought: no, such repetitions also should *not* be allowed.
> If a programmer, by mistake, would try to specify the argument value in
> a call, an explicit TypeError should be raised -- otherwise it'd become
> a trap (especially for beginners and absent-minded programmers).

I disagree. One of the main selling points of this feature for me is
that adding a few "hidden parameters" to a function does not change the
signature of the function. If you raise a TypeError when the name of a
hidden parameter is in kwargs this is a change in signature.
- Jacob