En Fri, 14 Sep 2007 20:16:36 -0300, Dan Bishop <[EMAIL PROTECTED]>
escribi�:
> On Sep 14, 9:30 am, Mark Morss <[EMAIL PROTECTED]> wrote:
>> I would like to construct a class that includes both the integers and
>> None. I desire that if x and y are elements of this class, and both
>> are integers, then arithmetic operations between them, such as x+y,
>> return the same result as integer addition. However if either x or y
>> is None, these operations return None.
>
> Rather than subclassing int, why not just make a singleton NaN object
> with overloaded arithmetic operators that all return NaN?
Like this:
class _NaN(object):
__instance = None
def __new__(cls):
if cls.__instance is None:
cls.__instance = super(_NaN, cls).__new__(cls)
return cls.__instance
__repr__ = __str__ = lambda self: 'NaN'
def unop(self): return self
def binop(self, other): return self
def terop(self, other, unused=None): return self
def false2(self, other): return False
def true2(self, other): return True
def notimpl(self): return NotImplemented
__abs__ = __invert__ = __neg__ = __pos__ = unop
__add__ = __and__ = __div__ = __divmod__ = __floordiv__ = __lshift__ =
__mod__ = __mul__ = __rshift__ = __or__ = __sub__ = __truediv__ = __xor__
= binop
__radd__ = __rand__ = __rdiv__ = __rdivmod__ = __rfloordiv__ =
__rlshift__ = __rmod__ = __rmul__ = __rpow__ = __rrshift__ = __ror__ =
__rsub__ = __rtruediv__ = __rxor__ = binop
__pow__ = terop
__lt__ = __le__ = __eq__ = __gt__ = __ge__ = false2
__ne__ = true2
del unop, binop, terop, false2, true2, notimpl
NaN = _NaN()
def test():
assert NaN + 1 is NaN
assert 1 & NaN is NaN
assert NaN * NaN is NaN
assert abs(NaN) is NaN
assert str(NaN)=="NaN"
assert repr(NaN)=="NaN"
assert not (NaN==NaN)
assert (NaN!=NaN)
assert not (NaN>NaN)
assert not (NaN<NaN)
assert not (NaN>=NaN)
assert not (NaN<=NaN)
assert not (NaN==1)
assert (NaN!=1)
assert not (NaN>1)
assert not (NaN<1)
assert not (NaN>=1)
assert not (NaN<=1)
assert not (1==NaN)
assert (1!=NaN)
assert not (1>NaN)
assert not (1<NaN)
assert not (1>=NaN)
assert not (1<=NaN)
assert cmp(NaN, 1)!=0
assert cmp(1, NaN)!=0
#assert cmp(NaN, NaN)!=0
assert NaN is _NaN()
assert NaN is type(NaN)()
test()
--
Gabriel Genellina
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