And how would you implement that without support from the compiler? Does it use a hook that catches the NameError? On Wed, Jun 29, 2016 at 11:15 AM, Brett Cannon wrote:

On Wed, 29 Jun 2016 at 10:41 Ethan Furman wrote:

...

There is a several-month-old request to add aenum's [1] AutoNumberEnum to the stdlib [2].

The requester and two of the three developers of Enum are in favor (the third hasn't chimed in yet).

This new addition would enable the following:

from Enum import AutoNumberEnum

class Color(AutoNumberEnum): # auto-number magic is on Red Green Blue Cyan # magic turns off when non-enum is defined

def is_primary(self): # typos in methods, etc, will raise return self in (self.Red, self.Grene, self.Blue)

# typos after the initial definition stanza will raise BlueGreen = Blue + Grene

There is, of course, the risk of typos during the initial member definition stanza, but since this magic only happens when the user explicitly asks for it (AutoNumberEnum), I think it is acceptable.

The `start` parameter is still available, and assigning a number is supported (subsequent numbers will (re)start from the assigned number).

Thoughts? Opinions? Flames?

Is it going to subclass Enum or IntEnum? Personally I would be quite happy to never have to specify a value for enums ever again, but only if they subclass Enum (since IntEnum is for compatibility with C stuff where a specific value is needed I don't think users need to mess that up by having the automatic numbering not work how they would expect).

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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 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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On 06/29/2016 01:01 PM, Ivan Levkivskyi wrote:

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,...?

Why would you want that? I remind you that this descends from Enum, so its members won't be directly interchangeable with ints. Presumably you want a bitfield enum, and those should descend from IntEnum. TBH I'd prefer the AutoNumberEnum *not* have this feature; it's already a little too magical for my tastes. //arry/

Why the 'start' parameter default is 1? 0 (zero) is more consistent with other parts of the language: indexes, enumerate, range... El mié., 29 de jun. de 2016 21:26, Ethan Furman escribió:

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~ _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/robertomartinezp%40gmail....

It may be worth mentioning that pandas Categoricals are mutable and zero-based: https://pandas-docs.github.io/pandas-docs-travis/categorical.html Serialization to SQL and CSV is (also?) lossy, though: - https://pandas-docs.github.io/pandas-docs-travis/categorical.html#getting-da... - https://pandas-docs.github.io/pandas-docs-travis/io.html#io-stata-categorica... On 06/29/2016 03:40 PM, Roberto Martínez wrote: Why the 'start' parameter default is 1? 0 (zero) is more consistent with

other parts of the language: indexes, enumerate, range...

An excerpt from [1]: The reason for defaulting to 1 as the starting number and not 0 is that 0

is False in a boolean sense, but enum members all evaluate to True.

-- ~Ethan~ [1] https://docs.python.org/3/library/enum.html#functional-api _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/wes.turner%40gmail.com