I should probably clarify that for this to work, Foo must derive from enum.Flags. See https://docs.python.org/3/library/enum.html#flag.

(Or enum.IntFlag, https://docs.python.org/3/library/enum.html#intflag.)

Note that when using Flag, you can name the "zero" value (Color.BLACK in the 3rd example). When using IntFlag, you just use 0.

On Sat, Dec 30, 2017 at 9:33 PM, Guido van Rossum <guido@python.org> wrote:

On Sat, Dec 30, 2017 at 8:50 PM, Franklin? Lee <leewangzhong+python@gmail.com> wrote:
Paddy might want something like this:
- For existing APIs which take int or IntFlag flags, allow them to
also take a set (or perhaps any collection) of flags.
- In new APIs, take sets of Enum flags, and don't make them IntFlag.
- Documentation should show preference toward using sets of Enum
flags. Tutorials should pass sets.

I'm not keen on this recommendation. An argument that takes a Set[Foo] would mean that in order to specify:
- no flags: you'd have to pass set() -- you can't use {} since that's an empty dict, not an empty set
- one flag: you'd have to pass {Foo.BAR} rather than just Foo.BAR
- two flags: you'd have to pass {Foo.BAR, Foo.BAZ} rather than Foo.BAR | Foo.BAZ

I think for each of these the proposal would be strictly worse than the current convention.

--
--Guido van Rossum (python.org/~guido)

--Guido van Rossum (python.org/~guido)