Cannot use functional API to create enum with zero values

[gerritholl]

BPO	30616
Nosy	@vstinner, @ethanfurman, @gerritholl
PRs	bpo-30616: Functional API of enum allows to create empty enums. #2304 [3.6] bpo-30616: Functional API of enum allows to create empty enums (#2304) #2324 [3.5] bpo-30616: Functional API of enum allows to create empty enums (#2304) #2888 [3.5] bpo-30616: Functional API of enum allows to create empty enums (#2304) #2889

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/ethanfurman'
closed_at = <Date 2017-08-17.08:57:32.952>
created_at = <Date 2017-06-09.17:30:17.874>
labels = ['3.7', 'library']
title = 'Cannot use functional API to create enum with zero values'
updated_at = <Date 2017-08-17.08:57:32.934>
user = 'https://github.com/gerritholl'

bugs.python.org fields:

activity = <Date 2017-08-17.08:57:32.934>
actor = 'vstinner'
assignee = 'ethan.furman'
closed = True
closed_date = <Date 2017-08-17.08:57:32.952>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2017-06-09.17:30:17.874>
creator = 'Gerrit.Holl'
dependencies = []
files = []
hgrepos = []
issue_num = 30616
keywords = []
message_count = 5.0
messages = ['295559', '296567', '296569', '296776', '300404']
nosy_count = 3.0
nosy_names = ['vstinner', 'ethan.furman', 'Gerrit.Holl']
pr_nums = ['2304', '2324', '2888', '2889']
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue30616'
versions = ['Python 3.6', 'Python 3.7']

[gerritholl]

The OO API allows to create empty enums, i.e. without any values. However, the functional API does not, as this will result in an IndexError as shown below:

In [1]: import enum

In [2]: class X(enum.IntFlag): pass

In [3]: Y = enum.IntFlag("Y", [])
---------------------------------------------------------------------------

IndexError                                Traceback (most recent call last)
<ipython-input-3-1fda5945e0b2> in <module>()
----> 1 Y = enum.IntFlag("Y", [])

~/lib/python3.6/enum.py in __call__(cls, value, names, module, qualname, type, start)
291 return cls.__new__(cls, value)
292 # otherwise, functional API: we're creating a new Enum type
--> 293 return cls._create_(value, names, module=module, qualname=qualname, type=type, start=start)
294
295 def __contains__(cls, member):

~/lib/python3.6/enum.py in _create_(cls, class_name, names, module, qualname, type, start)
382 if isinstance(names, str):
383 names = names.replace(',', ' ').split()
--> 384 if isinstance(names, (tuple, list)) and isinstance(names[0], str):
385 original_names, names = names, []
386 last_values = []

IndexError: list index out of range

[ethanfurman]

New changeset dcc8ce4 by ethanfurman (Dong-hee Na) in branch 'master':
bpo-30616: Functional API of enum allows to create empty enums. (bpo-2304)
dcc8ce4

[ethanfurman]

3.7 fixed, now need 3.6.

[ethanfurman]

New changeset 504b950 by ethanfurman (Dong-hee Na) in branch '3.6':
[3.6] bpo-30616: Functional API of enum allows to create empty enums. (bpo-2304) (bpo-2324)
504b950

[vstinner]

Thanks for the bugreport Gerrit Holl and thanks for fixes Dong-hee Na!