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gh-108682: [Enum] raise TypeError if super().__new__ called in custom __new__ (GH-108704)

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When overriding the `__new__` method of an enum, the underlying data type should be created directly; i.e. .

    member = object.__new__(cls)
    member = int.__new__(cls, value)
    member = str.__new__(cls, value)

Calling `super().__new__()` finds the lookup version of `Enum.__new__`, and will now raise an exception when detected.
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Ethan Furman 2023-08-31 12:45:12 -07:00 • committed by GitHub
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Doc/howto/enum.rst
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@ -426,10 +426,17 @@ enumeration, with the exception of special methods (:meth:`__str__`,
:meth:`__add__`, etc.), descriptors (methods are also descriptors), and
variable names listed in :attr:`_ignore_`.
Note: if your enumeration defines :meth:`__new__` and/or :meth:`__init__` then
Note: if your enumeration defines :meth:`__new__` and/or :meth:`__init__`,
any value(s) given to the enum member will be passed into those methods.
See `Planet`_ for an example.
.. note::
The :meth:`__new__` method, if defined, is used during creation of the Enum
members; it is then replaced by Enum's :meth:`__new__` which is used after
class creation for lookup of existing members. See :ref:`new-vs-init` for
more details.
Restricted Enum subclassing
---------------------------
@ -895,6 +902,8 @@ Some rules:
:meth:`__str__` method has been reset to their data types'
:meth:`__str__` method.
.. _new-vs-init:
When to use :meth:`__new__` vs. :meth:`__init__`
------------------------------------------------
@ -927,6 +936,11 @@ want one of them to be the value::
>>> print(Coordinate(3))
Coordinate.VY
.. warning::
*Do not* call ``super().__new__()``, as the lookup-only ``__new__`` is the one
that is found; instead, use the data type directly.
Finer Points
^^^^^^^^^^^^
@ -1353,6 +1367,13 @@ to handle any extra arguments::
members; it is then replaced by Enum's :meth:`__new__` which is used after
class creation for lookup of existing members.
.. warning::
*Do not* call ``super().__new__()``, as the lookup-only ``__new__`` is the one
that is found; instead, use the data type directly -- e.g.::
obj = int.__new__(cls, value)
OrderedEnum
^^^^^^^^^^^