Ensure unwanted names removed in class definition
Jussi Piitulainen
ei at kun.ei.invalid
Wed Aug 12 12:33:00 EDT 2015
Ben Finney writes:
> How can I ensure incidental names don't end up in the class
> definition, with code that works on both Python 2 and Python 3?
>
> With the following class definition, the incidental names `foo` and
> `bar`, only needed for the list comprehension, remain in the `Parrot`
> namespace::
>
> __metaclass__ = object
>
> class Parrot:
> """ A parrot with beautiful plumage. """
>
> plumage = [
> (foo, bar) for (foo, bar) in feathers.items()
> if bar == "beautiful"]
>
> assert hasattr(Parrot, 'plumage') # ← okay, has the wanted name
> assert not hasattr(Parrot, 'foo') # ← FAILS, has an unwanted name
> assert not hasattr(Parrot, 'bar') # ← FAILS, has an unwanted name
[- -]
> How can I write the class definition with the list comprehension and
> *not* keep the incidental names — in code that will run correctly on
> both Python 2 and Python 3?
Make them an implementation detail:
plumage = [
(__foo__, __bar__) for (__foo__, __bar__) in feathers.items()
if __bar__ == "beautiful" ]
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