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| Subject | Re: suppressing import errors |
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| From | David Riley <fraveydank@gmail.com> |
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| Date | Tue, 15 Nov 2011 16:20:33 -0500 |
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| To | Chris Angelico <rosuav@gmail.com> |
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On Nov 15, 2011, at 3:01 PM, Chris Angelico wrote:
> On Wed, Nov 16, 2011 at 6:39 AM, David Riley <fraveydank@gmail.com> 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
Back to comp.lang.python | Previous | Next — Next in thread | Find similar | Unroll thread
Re: suppressing import errors David Riley <fraveydank@gmail.com> - 2011-11-15 16:20 -0500
Re: suppressing import errors Alan Meyer <ameyer2@yahoo.com> - 2011-11-15 17:59 -0500
Re: suppressing import errors David Riley <fraveydank@gmail.com> - 2011-11-15 18:15 -0500
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