On Jan 9, 2008 12:04 AM, Mark Summerfield <[EMAIL PROTECTED]> wrote:
> I'm using this as a class decorator that fills in "missing" comparisons:
>
> def complete_comparisons(cls):
> class CompleteComparisonsError(Exception): pass
>
> if hasattr(cls.__lt__, "__objclass__"): # i.e. < inherited from object
> raise CompleteComparisonsError("{0} must define < and "
> "ideally ==".format(cls.__name__))
> if hasattr(cls.__eq__, "__objclass__"): # i.e. == inherited from object
> cls.__eq__ = lambda self, other: not (
> cls.__lt__(self, other) or cls.__lt__(other, self))
> cls.__ne__ = lambda self, other: not cls.__eq__(self, other)
> cls.__gt__ = lambda self, other: cls.__lt__(other, self)
> cls.__le__ = lambda self, other: (cls.__lt__(self, other) or
> cls.__eq__(self, other))
> cls.__ge__ = lambda self, other: (cls.__lt__(other, self) or
> cls.__eq__(self, other))
> return cls
>
>
> The reason for the ugly hasattr() calls is that object itself defines
> the comparison operators (in Python 3.0a2).
That's due to object's implementation of __eq__ and __ne__; this is
done by having a tp_richcompare slot and then the wrapper generator
adds wrappers for all six operators to the class dict. This is not
easy to fix.
--
--Guido van Rossum (home page: http://www.python.org/~guido/)
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