Ensure unwanted names removed in class definition

Chris Angelico rosuav at gmail.com
Wed Aug 12 11:14:30 CEST 2015


On Wed, Aug 12, 2015 at 7:01 PM, Ben Finney <ben+python at benfinney.id.au> wrote:
>     class Parrot:
>         """ A parrot with beautiful plumage. """
>
>         plumage = [
>                 (foo, bar) for (foo, bar) in feathers.items()
>                 if bar == "beautiful"]
>         del foo, bar  # ← FAILS, “NameError: name 'foo' is not defined”
>
> 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?

You could always do explicitly what a Py3 comprehension does, and wrap
it in a function:

plumage = (lambda: [
    (foo, bar) for (foo, bar) in feathers.items()
    if bar == "beautiful"])()

Hardly clean code, but it will work, and apart from having a redundant
layer of protection in Py3, will do exactly the same thing on both. Is
the lambda nesting cruft worth it?

ChrisA


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