[Python-Dev] AutoNumber Enum

[Ivan Levkivskyi]

It looks like the values in AutoNumberEnum are consecutive integers
1,2,3,...
Have you considered an option (keyword argument) to change this to powers
of two 1,2,4,8,...?

--
Ivan



On 29 June 2016 at 21:23, Ethan Furman <ethan at stoneleaf.us> wrote:

> 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~
>
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