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bpo-45331: [Enum] add rule to docs that mixin type must be subclassable (GH-30521)

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Nikita Sobolev 2022-01-11 02:42:45 +03:00 committed by GitHub
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Doc/howto/enum.rst
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@ -819,17 +819,20 @@ Some rules:
1. When subclassing :class:`Enum`, mix-in types must appear before
:class:`Enum` itself in the sequence of bases, as in the :class:`IntEnum`
example above.
2. While :class:`Enum` can have members of any type, once you mix in an
2. Mix-in types must be subclassable. For example,
:class:`bool` and :class:`range` are not subclassable
and will throw an error during Enum creation if used as the mix-in type.
3. While :class:`Enum` can have members of any type, once you mix in an
additional type, all the members must have values of that type, e.g.
:class:`int` above. This restriction does not apply to mix-ins which only
add methods and don't specify another type.
3. When another data type is mixed in, the :attr:`value` attribute is *not the
4. When another data type is mixed in, the :attr:`value` attribute is *not the
same* as the enum member itself, although it is equivalent and will compare
equal.
4. %-style formatting: `%s` and `%r` call the :class:`Enum` class's
5. %-style formatting: `%s` and `%r` call the :class:`Enum` class's
:meth:`__str__` and :meth:`__repr__` respectively; other codes (such as
`%i` or `%h` for IntEnum) treat the enum member as its mixed-in type.
5. :ref:`Formatted string literals <f-strings>`, :meth:`str.format`,
6. :ref:`Formatted string literals <f-strings>`, :meth:`str.format`,
and :func:`format` will use the mixed-in type's :meth:`__format__`
unless :meth:`__str__` or :meth:`__format__` is overridden in the subclass,
in which case the overridden methods or :class:`Enum` methods will be used.