On 2008-01-09, Christian Heimes wrote:
> Guido van Rossum wrote:
> > That's a different issue altogether (and your wish is not likely going
> > to be granted unless you write a PEP).
>
> You could write and implement a PEP about exposing the tp_richcompare
> slot to Python code.
>
> import sys
>
> class Example:
> def __richcmp__(self, other: object, op: int) -> bool:
> if op == sys.CMP_EQ:
> return self.value == other.value
> ...
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).
--
Mark Summerfield, Qtrac Ltd., www.qtrac.eu
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