[Python-Dev] pep 362 - 5th edition

[Yury Selivanov]

On 2012-06-19, at 11:55 AM, Ethan Furman wrote:

> Yury Selivanov wrote:
>> Hello,
>> The new revision of PEP 362 has been posted:
>> http://www.python.org/dev/peps/pep-0362/
>> Summary:
>> 1. What was 'Signature.__deepcopy__' is now 'Signature.__copy__'.
>> __copy__ creates a shallow copy of Signature, shallow copying its
>> Parameters as well.
>> 2. 'Signature.format()' was removed.  I think we'll add something
>> to customize formatting later, in 3.4.  Although, Signature still has
>> its __str__ method.
>> 3. Built-in ('C') functions no longer have mutable '__signature__'
>> attribute, that patch was reverted.  In the "Design Considerations"
>> section we stated clear that we don't support some callables.
>> 4. Positions of keyword-only parameters now longer affect equality
>> testing of Signatures, i.e. 'foo(*, a, b)' is equal to 'foo(*, b, a)'
>> (Thanks to Jim Jewett for pointing that out)
>> The only question we have now is:  when we do equality test between
>> Signatures, should we account for positional-only, var_positional
>> and var_keyword arguments names?  So that: 'foo(*args)' will
>> be equal to 'bar(*arguments)', but not to 'spam(*coordinates:int)'
>> (Again, I think that's a Jim's idea)
> 
> There are obviously cases where the names should be considered (such as foo(source, dest) and bar(dest, source) ) and cases where it should not be (spam(text, count) and eggs(txt, cnt) )...
> 
> I think the default implementation should be strict (names are considered) as it is safer to have a false negative than a false positive.

+1

> However, rather than force everyone who is willing to cope with the possible false positives from rewriting a Signature equality routine that ignores names, perhaps a method can be added to the class that does so?
> 
> class Signature:
>   . . .
>   def equivalent(self, other):
>      "compares two Signatures for equality (ignores parameter names)"
>      . . .

I don't think that comparing signatures will be a common operation,
so maybe we can postpone adding any additional methods for that?

-
Yury