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gh-143420: Clarify sequence behavior for slice indexes #143422

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gh-143420: Clarify sequence behavior for slice indexes #143422

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598ea16
gh-143420: Clarify sequence behavior for slice indexes
skirpichev Jan 5, 2026
f8737d8
Add reference to "Mutable Sequence Types" in array description
skirpichev Jan 6, 2026
3cd207d
Merge branch 'master' into improve-slice-notes/143420
skirpichev Jan 10, 2026
03732f9
address review: sequence -> mutable sequence
skirpichev Jan 10, 2026
5eef361
address review: reword note (4)
skirpichev Jan 10, 2026
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4 changes: 2 additions & 2 deletions Doc/library/array.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@
--------------

This module defines an object type which can compactly represent an array of
basic values: characters, integers, floating-point numbers. Arrays are sequence
basic values: characters, integers, floating-point numbers. Arrays are mutable :term:`sequence`
types and behave very much like lists, except that the type of objects stored in
them is constrained. The type is specified at object creation time by using a
:dfn:`type code`, which is a single character. The following type codes are
Expand Down Expand Up @@ -93,7 +93,7 @@ The module defines the following type:
otherwise, the initializer's iterator is passed to the :meth:`extend` method
to add initial items to the array.

Array objects support the ordinary sequence operations of indexing, slicing,
Array objects support the ordinary :ref:`mutable <typesseq-mutable>` :term:`sequence` operations of indexing, slicing,
concatenation, and multiplication. When using slice assignment, the assigned
value must be an array object with the same type code; in all other cases,
:exc:`TypeError` is raised. Array objects also implement the buffer interface,
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13 changes: 8 additions & 5 deletions Doc/library/stdtypes.rst
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Expand Up @@ -1093,11 +1093,14 @@ Notes:
still ``0``.

(4)
The slice of *s* from *i* to *j* is defined as the sequence of items with index
*k* such that ``i <= k < j``. If *i* or *j* is greater than ``len(s)``, use
``len(s)``. If *i* is omitted or ``None``, use ``0``. If *j* is omitted or
``None``, use ``len(s)``. If *i* is greater than or equal to *j*, the slice is
empty.
The slice of *s* from *i* to *j* is defined as the sequence of items with
index *k* such that ``i <= k < j``.

* If *i* is omitted or ``None``, use ``0``.
* If *j* is omitted or ``None``, use ``len(s)``.
* If *i* or *j* is less than ``-len(s)``, use ``0``.
* If *i* or *j* is greater than ``len(s)``, use ``len(s)``.
* If *i* is greater than or equal to *j*, the slice is empty.

(5)
The slice of *s* from *i* to *j* with step *k* is defined as the sequence of
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