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[Python-ideas] optional parameters

Devin Jeanpierre jeanpierreda at gmail.com
Wed Apr 16 19:59:37 CEST 2014 
On Wed, Apr 16, 2014 at 10:29 AM, Guido van Rossum <guido at python.org> wrote:
> TBH I think it's usually an anti-pattern when you have an API where the
> absence of a parameter is not equivalent to some default value. It makes
> wrapping such APIs awkward, e.g.
>
> def logging_foo(*, arg1='something_other_than_spam', arg3=None,
> arg4=<what???>):
>     loging.info('calling foo(arg1=%r, arg3=%r, arg4=%r)', arg1, arg3, arg4)
>     return foo(arg1=arg1, arg3=arg3, arg4=arg4)

Wrapping the APIs in such a tightly coupled way is already awkward,
since if the argspec (e.g. the default) changes, so must your wrapper.
*args/**kwargs are better when possible.

-- Devin

> On Wed, Apr 16, 2014 at 10:09 AM, Yury Selivanov <yselivanov.ml at gmail.com>
> wrote:
>>
>> Hello,
>>
>> There is a very common pattern for creating optional arguments
>> when you can't use None:
>>
>> _optional = object()
>> def foo(*, arg1='spam', arg3=None, arg4=_optional):
>>     if arg4 is _optional:
>>         # caller didn't pass *anything* for arg4
>>     else:
>>         # caller did pass some (maybe None) value for arg4
>>
>> It's a bit annoying to create this marker objects, and also,
>> if you try to render a signature of such function, you'll get
>> something like:
>>
>> "(*, arg1='spam', arg3=None, arg4=<object object at 0x104be7080>)"
>>
>> What if we add a standard marker for this use-case:
>> functools.optional or inspect.Parameter.optional?
>>
>>
>> Yury
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>
>
>
>
> --
> --Guido van Rossum (python.org/~guido)
>
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