[issue23591] Add Flags and IntFlags

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The name IntFlags is inspired by the Flags attribute in C# (this is the most close concept). The "Int" prefix is added for parallel with IntEnum and because the class behaves as int in some contexts (supports operators |, &, ^, ~ and can be passed to functions that require int). I don't know whether there is a need in Flags class that is not a subclass of int.

Other languages provide something like EnumSet - a specialized set of enums. But it has different interface.

1) If there are enum members FOO and BAR, their union is {FOO, BAR}, not FOO|BAR.
2) The union member itself is not a set.
3) A set can contain only predefined set of values (IntFlag allows non-defined bits be set).

If you thing that non-int flags could be useful, you can consider adding EnumSet for general enums and IntFlags (or just Flags) for int-like enums. But I think that new API can just use a set or a tuple of enums. IntFlags is needed for compatibility with old API or C API.

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<http://bugs.python.org/issue23591>
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