Names changed to protect the guilty

John J. Lee jjl at
Mon Oct 9 23:04:21 CEST 2006

aahz at (Aahz) writes:
> >I think I was reading the same code recently (epydoc?) and was also
> >momentarily horrified ;-) until I realized that it was quite
> >deliberately using three-valued logic (True, False, None) for some
> >presumably-sensible reason.  Since None is false, they had to use
> >"is".  So, given the need for three-valued logic, it's not as silly as
> >it looks.
> My take is that even in that case, one should use "is" only with None.
> There is too much ground for bugs with True/False, particularly if you
> either intend to work across version *or* you might possibly accept a
> user's object (because *they* might be working across versions and
> therefore returning 1/0 instead of True/False).  I think it's safest to
> simply ban this idiom.  No exceptions, never.

I tend to agree -- I think I'd define my own constants if I wanted a
three-valued logic for use with "is".


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