10000 bpo-45680: Improve docs on subscriptions w.r.t. `GenericAlias` objects by AlexWaygood · Pull Request #29479 · python/cpython · GitHub
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bpo-45680: Improve docs on subscriptions w.r.t. GenericAlias objects #29479

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Merged
merged 8 commits into from
Mar 8, 2022
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bpo-45680: Improve docs on subscriptions w.r.t. GenericAlias objects #29479

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5ae81b5
Improve docs on 'subscriptions'
AlexWaygood Nov 8, 2021
0dfaee5
Merge remote-tracking branch 'origin/main' into subscription-docs
AlexWaygood Nov 19, 2021
f3d66fc
Make this mergeable
AlexWaygood Nov 19, 2021
46f96c0
Reduce diff
AlexWaygood Dec 4, 2021
dc77393
Improve markup readability
AlexWaygood Dec 6, 2021
4ce0cb7
Merge remote-tracking branch 'origin/main' into subscription-docs
AlexWaygood Mar 5, 2022
5393008
Make more concise, improve technical accuracy
AlexWaygood Mar 5, 2022
19edeef
tweaks
AlexWaygood Mar 5, 2022
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Improve markup readability
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@AlexWaygood
AlexWaygood authored Dec 6, 2021
commit dc77393a7207a18cfecd88cf621c98f34caa0a68
12 changes: 6 additions & 6 deletions Doc/reference/expressions.rst
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Expand Up @@ -816,19 +816,19 @@ Subscriptions
pair: sequence; item

The subscription of an object in Python can have one of two effects. If the
object is a :term:`sequence` (such as a :class:`string<str>`,
object is a :term:`sequence` (such as a :class:`string <str>`,
:class:`tuple` or :class:`list`) or a :term:`mapping` (such as a
:class:`dictionary<dict>`), subscripting the object will select an object from
:class:`dictionary <dict>`), subscripting the object will select an object from
the collection. Subscripting certain *classes or types*, meanwhile, will
return a :ref:`generic alias <types-genericalias>` object representing a
*parameterized generic class*. The latter form of subscription is primarily
useful for :term:`type hinting<type hint>`.
useful for :term:`type hinting <type hint>`.

.. productionlist:: python-grammar
subscription: `primary` "[" `expression_list` "]"

The primary must evaluate to an object that supports subscription, such as a
:class:`list` or a :class:`dictionary<dict>`. User-defined objects can support
:class:`list` or a :class:`dictionary <dict>`. User-defined objects can support
subscription by defining one or both of :meth:`~object.__getitem__` and
:meth:`~object.__class_getitem__`.

Expand All @@ -852,7 +852,7 @@ via :meth:`~object.__getitem__`:
:class:`int` or a :class:`slice` (as discussed in the following section).

The formal syntax makes no special provision for negative indices in
:term:`sequences<sequence>`. However, built-in sequences all provide a :meth:`~object.__getitem__`
:term:`sequences <sequence>`. However, built-in sequences all provide a :meth:`~object.__getitem__`
method that interprets negative indices by adding the length of the sequence
to the index so that, for example, ``x[-1]`` selects the last item of ``x``. The
resulting value must be a nonnegative integer less than the number of items in
Expand All @@ -865,7 +865,7 @@ this method will need to explicitly add that support.
single: character
pair: string; item

A :class:`string<str>` is a special kind of sequence whose items are
A :class:`string <str>` is a special kind of sequence whose items are
*characters*. A character is not a separate data type but a string of exactly
one character.

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