On Nov 15, 2011, at 3:01 PM, Chris Angelico wrote:
> On Wed, Nov 16, 2011 at 6:39 AM, David Riley <[email protected]> wrote:
>> True, and that does avoid polluting namespace. However, you shouldn't be
>> testing for None as a bool; you should instead do an "if <module> is None:"
>> (or, of course, "is not None").
>
> Why not? Is there some other way for the module object to evaluate as false?
Well, probably not. It was my understanding that "None" evaluating to a
Boolean false was not necessarily guaranteed; I've even gotten some warnings
from Python to that effect, though I can't recall the context in which that
happened. In any case, PEP 8 states:
Comparisons to singletons like None should always be done with
'is' or 'is not', never the equality operators.
Also, beware of writing "if x" when you really mean "if x is not None"
-- e.g. when testing whether a variable or argument that defaults to
None was set to some other value. The other value might have a type
(such as a container) that could be false in a boolean context!
Obviously, that last bit doesn't apply to modules; they're not going to
evaluate as False in general. I just bristle when I see people writing "if x"
when they really mean "if x is not None", perhaps because it's not The Right
Way(tm)? It mostly comes down to aesthetics, I guess. Write what you really
mean.
- Dave
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