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| -rw-r--r-- | Doc/library/enum.rst | 31 | ||||
| -rw-r--r-- | Misc/ACKS | 1 |
2 files changed, 32 insertions, 0 deletions
diff --git a/Doc/library/enum.rst b/Doc/library/enum.rst index 3f17f99476..6408c01060 100644 --- a/Doc/library/enum.rst +++ b/Doc/library/enum.rst @@ -736,6 +736,37 @@ Some rules: type's :meth:`__format__`. If the :class:`Enum` class's :func:`str` or :func:`repr` is desired, use the `!s` or `!r` format codes. +When to use :meth:`__new__` vs. :meth:`__init__` +------------------------------------------------ + +:meth:`__new__` must be used whenever you want to customize the actual value of +the :class:`Enum` member. Any other modifications may go in either +:meth:`__new__` or :meth:`__init__`, with :meth:`__init__` being preferred. + +For example, if you want to pass several items to the constructor, but only +want one of them to be the value:: + + >>> class Coordinate(bytes, Enum): + ... """ + ... Coordinate with binary codes that can be indexed by the int code. + ... """ + ... def __new__(cls, value, label, unit): + ... obj = bytes.__new__(cls, [value]) + ... obj._value_ = value + ... obj.label = label + ... obj.unit = unit + ... return obj + ... PX = (0, 'P.X', 'km') + ... PY = (1, 'P.Y', 'km') + ... VX = (2, 'V.X', 'km/s') + ... VY = (3, 'V.Y', 'km/s') + ... + + >>> print(Coordinate['PY']) + Coordinate.PY + + >>> print(Coordinate(3)) + Coordinate.VY Interesting examples -------------------- @@ -68,6 +68,7 @@ Ammar Askar Neil Aspinall Chris AtLee Aymeric Augustin +Andres Ayala Cathy Avery John Aycock Donovan Baarda |