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PEP 655: Motivation: Enables mixed key requiredness in the TypedDict alternative syntax #2359

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PEP 655: Motivation: Enables mixed key requiredness in the TypedDict alternative syntax #2359

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PEP 655: Motivation: Enables mixed key requiredness in the TypedDict …
davidfstr Feb 23, 2022
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Change "alternative syntax" -> "alternative functional syntax" at fir…
davidfstr Feb 23, 2022
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Update pep-0655.rst
davidfstr Feb 25, 2022
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18 changes: 16 additions & 2 deletions pep-0655.rst
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Expand Up @@ -55,12 +55,26 @@ a mix of both required and potentially-missing keys:
title: str
year: NotRequired[int]

This PEP also makes it possible to define TypedDicts in the
:pep:`alternative functional syntax <589#alternative-syntax>`
with a mix of required and potentially-missing keys,
which is not currently possible at all because the alternative syntax does
not support inheritance:

::
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Actor = TypedDict('Actor', {
'name': str,
# "in" is a keyword, so the functional syntax is necessary
'in': NotRequired[List[str]],
})


Rationale
=========

One might think it unusual to propose syntax that prioritizes marking
*required* keys rather than syntax for *potentially-missing* keys, as is
*required* keys rather than *potentially-missing* keys, as is
customary in other languages like TypeScript:

.. code-block:: typescript
Expand Down Expand Up @@ -139,7 +153,7 @@ same time:
year: NotRequired[Required[int]] # ERROR


The :pep:`alternative syntax <589#alternative-syntax>`
The :pep:`alternative functional syntax <589#alternative-syntax>`
for TypedDict also supports
``Required[]`` and ``NotRequired[]``:

Expand Down