Ensure unwanted names removed in class definition
Ben Finney
ben+python at benfinney.id.au
Wed Aug 12 05:01:05 EDT 2015
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
So I can remove those names after using them::
__metaclass__ = object
class Parrot:
""" A parrot with beautiful plumage. """
plumage = [
(foo, bar) for (foo, bar) in feathers.items()
if bar == "beautiful"]
del foo, bar
assert hasattr(Parrot, 'plumage') # ← okay, has the wanted name
assert not hasattr(Parrot, 'foo') # ← okay, no unwanted name
assert not hasattr(Parrot, 'bar') # ← okay, no unwanted name
But that fails on Python 3, since the names *don't* persist from the
list comprehension:
__metaclass__ = object
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?
--
\ “Pinky, are you pondering what I'm pondering?” “Well, I think |
`\ so, but *where* do you stick the feather and call it macaroni?” |
_o__) —_Pinky and The Brain_ |
Ben Finney
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