On 06/29/2016 12:11 PM, Guido van Rossum wrote:
And how would you implement that without support from the compiler? Does it use a hook that catches the NameError?
It's built into the _EnumDict class dictionary used during class creation. Current (edited) code from the aenum package that implements this: class _EnumDict(dict): """Track enum member order and ensure member names are not reused. EnumMeta will use the names found in self._member_names as the enumeration member names. """ def __init__(self, locked=True, start=1, multivalue=False): super(_EnumDict, self).__init__() # list of enum members self._member_names = [] # starting value for AutoNumber self._value = start - 1 # when the magic turns off self._locked = locked ... def __getitem__(self, key): if ( self._locked or key in self or _is_sunder(key) or _is_dunder(key) ): return super(_EnumDict, self).__getitem__(key) try: # try to generate the next value value = self._value + 1 self.__setitem__(key, value) return value except: # couldn't work the magic, report error raise KeyError('%s not found' % key) def __setitem__(self, key, value): """Changes anything not sundured, dundered, nor a descriptor. Single underscore (sunder) names are reserved. """ if _is_sunder(key): raise ValueError('_names_ are reserved for future Enum use') elif _is_dunder(key): if key == '__order__': key = '_order_' if _is_descriptor(value): self._locked = True elif key in self._member_names: # descriptor overwriting an enum? raise TypeError('Attempted to reuse name: %r' % key) elif not _is_descriptor(value): if key in self: # enum overwriting a descriptor? raise TypeError('%s already defined as: %r' % ... self._member_names.append(key) if not self._locked: if isinstance(value, int): self._value = value else: count = self._value + 1 self._value = count value = count, value else: # not a new member, turn off the autoassign magic self._locked = True super(_EnumDict, self).__setitem__(key, value) Disclaimer: some errors may have crept in as I deleted unrelated content. For the full code check out the _EnumDict class in the aenum package. -- ~Ethan~