On 2015-08-12 10:01, Ben Finney wrote:
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?
Have you thought about catching the NameError? -- https://mail.python.org/mailman/listinfo/python-list
