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This issue will track implementation of PEP 362 functionality.

Signature and signature are two variable names that differ only in case.
To avoid confusion, I recommend one of the names should be changed.

Well, 'Signature' class is unlikely to be used very frequently. So I think it's fine.

Yes, it seems quite common to me to have a class called Thing and instances named thing. Unless it makes the code wrap better, using real names like signature instead of for example sig is recommended by PEP 8.

Attaching a patch that implements the latest version of the PEP.
Quick summary:
1. Ditched Signature.name & Signature.qualname
2. Added Signature.__eq__ and __ne__
3. signature() supports classes, metaclasses, decorated stuff, partials, methods, classmethods, callable objects etc
4. signature() does a deepcopy of __signature__ attribute if
there is one
5. No implicit caching anywhere
6. Signature.format(...) and Signature.__str__
7. Signature.bind_partial

Attaching the new version of the patch.
Summary:
1. 'is_*' family was replaced with 'Parameter.kind'
2. 'signature()' function was updated to check for '__wrapped__' 
attribute in all callables
3. 'is_implemented' -> 'implemented'
4. Added support for POSITIONAL_ONLY parameters (in 'bind()')

One small thing: can we find a name for the function that starts with a verb? It’s the recommended naming style for functions, and would help making a difference between the class and the function. I also expect people to use "signature" and "sig" for their instances.

New version (pep363.4.patch)
Summary:
1. Removed 'Signature.implemented'
2. No more patching built-ins - no issues with shared interpreters
3. Removed 'Signature.format()'. If needed we'll reintroduce it in 3.4 (although we still have 'Signature.__str__')
4. Signature now implements just __copy__ - creates a shallow copy (__deepcopy__ has been removed, as it wasn't deep)
5. Signature.__eq__ fixed to ignore order of keyword-only arguments.
Thanks and please review!

Eric,
I personally prefer simple 'signature()' more than 'get_signature()'. But I'll ask this question on python-dev on the next PEP update.

New patch (pep362.5.patch)
Fixed a bug in BoundArguments.args & BoundArguments.kwargs

I left a few comments on rietveld.
The '\' is sometimes used where not necessary and the preferred way to write conditions on multiple lines is:
(foo == bar and
 bar == baz and
 baz == asd)
rather than
foo == bar \
 and bar == baz \
 and baz == asd
Have you measured the coverage of the tests?

New patch - pep362.6.patch
Ezio,
I've eliminated almost all '\'.
Test coverage is now almost 100%.

New patch - pep362.7.patch
Summary:
1. Signature & Parameter objects are now immutable
2. Signature.replace() and Parameter.replace()
3. Signature has a new default constructor, which
accepts parameters list and a return_annotation; and
a new 'from_function', which create a Signature object
for the passed function.
4. Parameter.__str__
The implementation has 100% test coverage and is stable.
Please review.
Thanks!

New patch - pep362.8.patch
One big change (Guido's request) - No more AttributeErrors on missing Parameter.default of Signature.return_annotation. They now will be set to Parameter.empty & Signature.empty correspondingly.

New changeset d892bf410478 by Larry Hastings in branch 'default':
Issue #15008: Implement PEP 362 "Signature Objects".
http://hg.python.org/cpython/rev/d892bf410478 

Are we going to get documentation?

Benjamin: http://bugs.python.org/issue15151