Issue 31801: vars() manipulation encounters problems with Enum

The following code should work (from https://stackoverflow.com/a/46780742/208880):


    class BaudRate(Enum):

        cls = vars()
        regexp = r"(?:^|,)B(?P<rate>\d+)"
        rates = sorted(map(int, re.findall(regexp, ",".join(dir(termios)))))
        for value in rates:
            cls['B%d' % value] = value

        @classmethod
        def valid_rate(cls, value):
            return (any(value == item.value for item in cls))


This doesn't work because EnumMeta does not allow names to be reassigned nor deleted.  aenum gets around this by allowing an _ignore_ attribute which contains the names that should not be tracked (and, in fact, those names are removed from the final class).

Unless a better idea is put forward, I will add _ignore_ support to Enum.

Not necessarily an argument against this feature, but two workarounds exist for this already:


1. Use `nonlocal` to prevent `value` going into the class namespace:

    value = None
    
    class BaudRate(enum.Enum):    
        nonlocal value
        for value in rates:
            locals()['B%d' % value] = value
    
        @classmethod
        def valid_rate(cls, value):
            return (any(value == item.value for item in cls))

2. Use `types.new_class`, which is more suited to dynamic class creation anyway:

    def make_cls(ns):
        for value in rates:
            ns['B%d' % value] = value

        @classmethod
        def valid_rate(cls, value):
            return (any(value == item.value for item in cls))

        ns['valid_rate'] = valid_rate

    types.new_class('BaudRate', (enum.Enum,), exec_body=make_cls)

New changeset a4b1bb4801f7a941ff9e86b96da539be1c288833 by Ethan Furman in branch 'master':
bpo-31801:  Enum:  add _ignore_ as class option (#5237)
https://github.com/python/cpython/commit/a4b1bb4801f7a941ff9e86b96da539be1c288833