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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 1. When subclassing :class:`Enum`, mix-in types must appear before
:class:`Enum` itself in the sequence of bases, as in the :class:`IntEnum` :class:`Enum` itself in the sequence of bases, as in the :class:`IntEnum`
example above. 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. 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 :class:`int` above. This restriction does not apply to mix-ins which only
add methods and don't specify another type. 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 same* as the enum member itself, although it is equivalent and will compare
equal. 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 :meth:`__str__` and :meth:`__repr__` respectively; other codes (such as
`%i` or `%h` for IntEnum) treat the enum member as its mixed-in type. `%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__` and :func:`format` will use the mixed-in type's :meth:`__format__`
unless :meth:`__str__` or :meth:`__format__` is overridden in the subclass, unless :meth:`__str__` or :meth:`__format__` is overridden in the subclass,
in which case the overridden methods or :class:`Enum` methods will be used. in which case the overridden methods or :class:`Enum` methods will be used.