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Hopefully clarify the difference between Optional[t] and an optional argument.

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Guido van Rossum 2016-02-10 09:48:58 -08:00
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Doc/library/typing.rst
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@ -286,6 +286,13 @@ The module defines the following classes, functions and decorators:
``Optional[X]`` is equivalent to ``Union[X, type(None)]``.
Note that this is not the same concept as an optional argument,
which is one that has a default. An optional argument with a
default needn't use the ``Optional`` qualifier on its type
annotation (although it is inferred if the default is ``None``).
A mandatory argument may still have an ``Optional`` type if an
explicit value of ``None`` is allowed.
.. class:: Tuple
Tuple type; ``Tuple[X, Y]`` is the is the type of a tuple of two items