[Python-Dev] Updated PEP 362 (Function Signature Object) (original) (raw)

Larry Hastings larry at hastings.org
Wed Jun 6 18:05:48 CEST 2012

On 06/06/2012 08:38 AM, Steven D'Aprano wrote:

What's the fully qualified name of the function, and why is it needed?

Please see PEP 3155.

"args" is just a common name for the parameter, not for the kind of parameter. *args (or *data, *whatever) is a varargs parameter, and so the attribute should be called "isvarargs". [...] Likewise for **kwargs (or **kw, etc.)

Yury will be pleased; those were his original names. I argued for "is_args" and "is_kwargs".

I assert that "args" and "kwargs" are not merely "common name[s] for the parameter[s]", they are The Convention. Any seasoned Python programmer examining a Signature object who sees "is_args" and "is_kwargs" will understand immediately what they are. Jamming "var" in the middle of these names does not make their meaning any clearer--in fact I suggest it only detracts from readability.

Is there a use-case for isimplemented?

Yes, see issue 14626.

What happens when the existing function metadata and the signature object disagree?

Are there use-cases where we want them to disagree, or is disagreement always a sign that something is broken? [...] "Changes to the Signature object, or to any of its data members, do not affect the function itself." which leaves the possibility that signature may no longer match the actual argument spec, for some reason. If you remove getfullargspec, people will have to reinvent it to deal with such cases.

There's no reason why they should disagree. The "some reason" would be if some doorknob decided to change it--the objects are mutable, because there's no good reason to make them immutable.

We just wanted to be explicit, that information flowed from the callable to the Signature and never the other way 'round.

As for "what would happen", nothing good. My advice: don't change Signature objects for no reason.

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