Expand Up @@ -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 -------------------- Expand Down