[Python-ideas] Fwd: Extremely weird itertools.permutations

[Tim Peters]

[Tim]
>> 2. Making "equality" pluggable.  Your later algorithm bought "find
>> equivalence classes" speed for hashable elements by using a dict, but
>> a dict's notion of equality can't be changed.  So, make equality
>> pluggable, and that startup-time speed advantage vanishes for all but
>> operator.__eq__'s idea of equality.

[Oscar Benjamin]
> It sounds like you want Antoine's TransformDict:
> http://www.python.org/dev/peps/pep-0455/

Not really in this case - I want a two-argument function ("are A and B
equal?").  Not all plausible cases of that can be mapped to a
canonical hashable key.  For example, consider permutations of a list
of lists, where the user doesn't want int and float elements of the
lists to be considered equal when they happen to have the same value.
Is that a stretch?  Oh ya ;-)