[issue20632] Define a new __key__ protocol

[Nick Coghlan]

Nick Coghlan added the comment:

I suspect it could just be a class decorator (along the lines of
total_ordering), and it should certainly be prototyped on PyPI as such a
decorator (using a different name for the key calculating method). If it
eventually happened, elevation to a core protocol would really be about
defining this as being *preferred* in the cases where it applies, and
that's a fairly weak basis for changing the type constructor.

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<http://bugs.python.org/issue20632>
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