[Python-Dev] pep 362 - 5th edition

[Ethan Furman]

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.

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)"
       . . .

~Ethan~