A newbie question about class

[Joshua Muskovitz]

> > Could you explain a little more why "is not" is better than "!="?
>
> The short answer is that I don't think comparing something to None by
> identity will ever raise an error.  Comparing it by magnitude might.
>
> Python allows you to override magnitude comparison methods:  ==, !=, <, >,
> <=, >=.  If you are using code written by somebody else, you don't know
> whether they've accounted for comparison to None in their comparison
> methods.  If you compare to None by identity, you bypass that whole issue
> because comparison by identity ("is" and "is not") happens via id() and
> that's not something you can override (as far as I know).

And yet, unless you do use things like "!= None", bugs in packages like
FixedPoint would propogate.  It's a double edged sword.  Being able to use
"is not None" is a good way to be able to work around a bug like this (if
you don't have access to the source, for example), but I would hesitate to
say that it is "better".

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