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

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

3.7 fixed, now need 3.6.

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

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