GH-138465: Improve documentation for common sequence methods (#138474)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
This commit is contained in:
Adam Turner
2025-09-05 20:55:02 +01:00
committed by GitHub
parent e5c5830079
commit 8ed1d53e62
20 changed files with 187 additions and 125 deletions

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@@ -245,7 +245,6 @@ nitpick_ignore += [
('py:attr', '__annotations__'),
('py:meth', '__missing__'),
('py:attr', '__wrapped__'),
('py:meth', 'index'), # list.index, tuple.index, etc.
]
# gh-106948: Copy standard C types declared in the "c:type" domain and C

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@@ -591,9 +591,9 @@ exhaustive test suites that exercise every line of code in a module.
An appropriate testing discipline can help build large complex applications in
Python as well as having interface specifications would. In fact, it can be
better because an interface specification cannot test certain properties of a
program. For example, the :meth:`!list.append` method is expected to add new elements
program. For example, the :meth:`list.append` method is expected to add new elements
to the end of some internal list; an interface specification cannot test that
your :meth:`!list.append` implementation will actually do this correctly, but it's
your :meth:`list.append` implementation will actually do this correctly, but it's
trivial to check this property in a test suite.
Writing test suites is very helpful, and you might want to design your code to

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@@ -454,7 +454,7 @@ There are two factors that produce this result:
(the list), and both ``x`` and ``y`` refer to it.
2) Lists are :term:`mutable`, which means that you can change their content.
After the call to :meth:`!append`, the content of the mutable object has
After the call to :meth:`~sequence.append`, the content of the mutable object has
changed from ``[]`` to ``[10]``. Since both the variables refer to the same
object, using either name accesses the modified value ``[10]``.
@@ -1397,9 +1397,9 @@ To see why this happens, you need to know that (a) if an object implements an
:meth:`~object.__iadd__` magic method, it gets called when the ``+=`` augmented
assignment
is executed, and its return value is what gets used in the assignment statement;
and (b) for lists, :meth:`!__iadd__` is equivalent to calling :meth:`!extend` on the list
and returning the list. That's why we say that for lists, ``+=`` is a
"shorthand" for :meth:`!list.extend`::
and (b) for lists, :meth:`!__iadd__` is equivalent to calling
:meth:`~sequence.extend` on the list and returning the list.
That's why we say that for lists, ``+=`` is a "shorthand" for :meth:`list.extend`::
>>> a_list = []
>>> a_list += [1]

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@@ -1251,8 +1251,9 @@ Glossary
The :class:`collections.abc.Sequence` abstract base class
defines a much richer interface that goes beyond just
:meth:`~object.__getitem__` and :meth:`~object.__len__`, adding
:meth:`!count`, :meth:`!index`, :meth:`~object.__contains__`, and
:meth:`~object.__reversed__`. Types that implement this expanded
:meth:`~sequence.count`, :meth:`~sequence.index`,
:meth:`~object.__contains__`, and :meth:`~object.__reversed__`.
Types that implement this expanded
interface can be registered explicitly using
:func:`~abc.ABCMeta.register`. For more documentation on sequence
methods generally, see

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@@ -83,7 +83,7 @@ The following functions are provided:
Insert *x* in *a* in sorted order.
This function first runs :py:func:`~bisect.bisect_left` to locate an insertion point.
Next, it runs the :meth:`!insert` method on *a* to insert *x* at the
Next, it runs the :meth:`~sequence.insert` method on *a* to insert *x* at the
appropriate position to maintain sort order.
To support inserting records in a table, the *key* function (if any) is
@@ -103,7 +103,7 @@ The following functions are provided:
entries of *x*.
This function first runs :py:func:`~bisect.bisect_right` to locate an insertion point.
Next, it runs the :meth:`!insert` method on *a* to insert *x* at the
Next, it runs the :meth:`~sequence.insert` method on *a* to insert *x* at the
appropriate position to maintain sort order.
To support inserting records in a table, the *key* function (if any) is

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@@ -264,8 +264,9 @@ Collections Abstract Base Classes -- Detailed Descriptions
ABCs for read-only and mutable :term:`sequences <sequence>`.
Implementation note: Some of the mixin methods, such as
:meth:`~container.__iter__`, :meth:`~object.__reversed__` and :meth:`index`, make
repeated calls to the underlying :meth:`~object.__getitem__` method.
:meth:`~container.__iter__`, :meth:`~object.__reversed__`,
and :meth:`~sequence.index` make repeated calls to the underlying
:meth:`~object.__getitem__` method.
Consequently, if :meth:`~object.__getitem__` is implemented with constant
access speed, the mixin methods will have linear performance;
however, if the underlying method is linear (as it would be with a
@@ -281,8 +282,8 @@ Collections Abstract Base Classes -- Detailed Descriptions
Supporting the *start* and *stop* arguments is optional, but recommended.
.. versionchanged:: 3.5
The :meth:`!index` method added support for *stop* and *start*
arguments.
The :meth:`~sequence.index` method gained support for
the *stop* and *start* arguments.
.. class:: Set
MutableSet

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@@ -783,10 +783,10 @@ sequence of key-value pairs into a dictionary of lists:
When each key is encountered for the first time, it is not already in the
mapping; so an entry is automatically created using the :attr:`~defaultdict.default_factory`
function which returns an empty :class:`list`. The :meth:`!list.append`
function which returns an empty :class:`list`. The :meth:`list.append`
operation then attaches the value to the new list. When keys are encountered
again, the look-up proceeds normally (returning the list for that key) and the
:meth:`!list.append` operation adds another value to the list. This technique is
:meth:`list.append` operation adds another value to the list. This technique is
simpler and faster than an equivalent technique using :meth:`dict.setdefault`:
>>> d = {}

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@@ -732,8 +732,8 @@ or both.
These items will be appended to the object either using
``obj.append(item)`` or, in batch, using ``obj.extend(list_of_items)``.
This is primarily used for list subclasses, but may be used by other
classes as long as they have
:ref:`append and extend methods <typesseq-common>` with
classes as long as they have :meth:`~sequence.append`
and :meth:`~sequence.extend` methods with
the appropriate signature. (Whether :meth:`!append` or :meth:`!extend` is
used depends on which pickle protocol version is used as well as the number
of items to append, so both must be supported.)

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@@ -1000,8 +1000,6 @@ operations have the same priority as the corresponding numeric operations. [3]_
pair: slice; operation
pair: operator; in
pair: operator; not in
single: count() (sequence method)
single: index() (sequence method)
+--------------------------+--------------------------------+----------+
| Operation | Result | Notes |
@@ -1018,7 +1016,7 @@ operations have the same priority as the corresponding numeric operations. [3]_
| ``s * n`` or | equivalent to adding *s* to | (2)(7) |
| ``n * s`` | itself *n* times | |
+--------------------------+--------------------------------+----------+
| ``s[i]`` | *i*\ th item of *s*, origin 0 | (3)(9) |
| ``s[i]`` | *i*\ th item of *s*, origin 0 | (3)(8) |
+--------------------------+--------------------------------+----------+
| ``s[i:j]`` | slice of *s* from *i* to *j* | (3)(4) |
+--------------------------+--------------------------------+----------+
@@ -1031,13 +1029,6 @@ operations have the same priority as the corresponding numeric operations. [3]_
+--------------------------+--------------------------------+----------+
| ``max(s)`` | largest item of *s* | |
+--------------------------+--------------------------------+----------+
| ``s.index(x[, i[, j]])`` | index of the first occurrence | \(8) |
| | of *x* in *s* (at or after | |
| | index *i* and before index *j*)| |
+--------------------------+--------------------------------+----------+
| ``s.count(x)`` | total number of occurrences of | |
| | *x* in *s* | |
+--------------------------+--------------------------------+----------+
Sequences of the same type also support comparisons. In particular, tuples
and lists are compared lexicographically by comparing corresponding elements.
@@ -1143,16 +1134,42 @@ Notes:
concatenation or repetition.
(8)
``index`` raises :exc:`ValueError` when *x* is not found in *s*.
Not all implementations support passing the additional arguments *i* and *j*.
These arguments allow efficient searching of subsections of the sequence. Passing
the extra arguments is roughly equivalent to using ``s[i:j].index(x)``, only
without copying any data and with the returned index being relative to
the start of the sequence rather than the start of the slice.
(9)
An :exc:`IndexError` is raised if *i* is outside the sequence range.
.. rubric:: Sequence Methods
Sequence types also support the following methods:
.. method:: list.count(value, /)
range.count(value, /)
tuple.count(value, /)
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.count(value, /)
Return the total number of occurrences of *value* in *sequence*.
.. method:: list.index(value[, start[, stop])
range.index(value[, start[, stop])
tuple.index(value[, start[, stop])
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.index(value[, start[, stop])
Return the index of the first occurrence of *value* in *sequence*.
Raises :exc:`ValueError` if *value* is not found in *sequence*.
The *start* or *stop* arguments allow for efficient searching
of subsections of the sequence, beginning at *start* and ending at *stop*.
This is roughly equivalent to ``start + sequence[start:stop].index(value)``,
only without copying any data.
.. caution::
Not all sequence types support passing the *start* and *stop* arguments.
.. _typesseq-immutable:
@@ -1202,14 +1219,6 @@ accepts integers that meet the value restriction ``0 <= x <= 255``).
pair: subscript; assignment
pair: slice; assignment
pair: statement; del
single: append() (sequence method)
single: clear() (sequence method)
single: copy() (sequence method)
single: extend() (sequence method)
single: insert() (sequence method)
single: pop() (sequence method)
single: remove() (sequence method)
single: reverse() (sequence method)
+------------------------------+--------------------------------+---------------------+
| Operation | Result | Notes |
@@ -1233,39 +1242,14 @@ accepts integers that meet the value restriction ``0 <= x <= 255``).
| ``del s[i:j:k]`` | removes the elements of | |
| | ``s[i:j:k]`` from the list | |
+------------------------------+--------------------------------+---------------------+
| ``s.append(x)`` | appends *x* to the end of the | |
| | sequence (same as | |
| | ``s[len(s):len(s)] = [x]``) | |
+------------------------------+--------------------------------+---------------------+
| ``s.clear()`` | removes all items from *s* | \(5) |
| | (same as ``del s[:]``) | |
+------------------------------+--------------------------------+---------------------+
| ``s.copy()`` | creates a shallow copy of *s* | \(5) |
| | (same as ``s[:]``) | |
+------------------------------+--------------------------------+---------------------+
| ``s.extend(t)`` or | extends *s* with the | |
| ``s += t`` | contents of *t* (for the | |
| ``s += t`` | extends *s* with the | |
| | contents of *t* (for the | |
| | most part the same as | |
| | ``s[len(s):len(s)] = t``) | |
+------------------------------+--------------------------------+---------------------+
| ``s *= n`` | updates *s* with its contents | \(6) |
| ``s *= n`` | updates *s* with its contents | \(2) |
| | repeated *n* times | |
+------------------------------+--------------------------------+---------------------+
| ``s.insert(i, x)`` | inserts *x* into *s* at the | |
| | index given by *i* | |
| | (same as ``s[i:i] = [x]``) | |
+------------------------------+--------------------------------+---------------------+
| ``s.pop()`` or ``s.pop(i)`` | retrieves the item at *i* and | \(2) |
| | also removes it from *s* | |
+------------------------------+--------------------------------+---------------------+
| ``s.remove(x)`` | removes the first item from | \(3) |
| | *s* where ``s[i]`` is equal to | |
| | *x* | |
+------------------------------+--------------------------------+---------------------+
| ``s.reverse()`` | reverses the items of *s* in | \(4) |
| | place | |
+------------------------------+--------------------------------+---------------------+
Notes:
@@ -1273,33 +1257,106 @@ Notes:
If *k* is not equal to ``1``, *t* must have the same length as the slice it is replacing.
(2)
The optional argument *i* defaults to ``-1``, so that by default the last
item is removed and returned.
(3)
:meth:`remove` raises :exc:`ValueError` when *x* is not found in *s*.
(4)
The :meth:`reverse` method modifies the sequence in place for economy of
space when reversing a large sequence. To remind users that it operates by
side effect, it does not return the reversed sequence.
(5)
:meth:`clear` and :meth:`!copy` are included for consistency with the
interfaces of mutable containers that don't support slicing operations
(such as :class:`dict` and :class:`set`). :meth:`!copy` is not part of the
:class:`collections.abc.MutableSequence` ABC, but most concrete
mutable sequence classes provide it.
.. versionadded:: 3.3
:meth:`clear` and :meth:`!copy` methods.
(6)
The value *n* is an integer, or an object implementing
:meth:`~object.__index__`. Zero and negative values of *n* clear
the sequence. Items in the sequence are not copied; they are referenced
multiple times, as explained for ``s * n`` under :ref:`typesseq-common`.
.. rubric:: Mutable Sequence Methods
Mutable sequence types also support the following methods:
.. method:: bytearray.append(value, /)
list.append(value, /)
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.append(value, /)
Append *value* to the end of the sequence
This is equivalent to writing ``seq[len(seq):len(seq)] = [value]``.
.. method:: bytearray.clear()
list.clear()
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.clear()
.. versionadded:: 3.3
Remove all items from *sequence*.
This is equivalent to writing ``del sequence[:]``.
.. method:: bytearray.copy()
list.copy()
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.copy()
.. versionadded:: 3.3
Create a shallow copy of *sequence*.
This is equivalent to writing ``sequence[:]``.
.. hint:: The :meth:`!copy` method is not part of the
:class:`~collections.abc.MutableSequence` :class:`~abc.ABC`,
but most concrete mutable sequence types provide it.
.. method:: bytearray.extend(iterable, /)
list.extend(iterable, /)
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.extend(iterable, /)
Extend *sequence* with the contents of *iterable*.
For the most part, this is the same as writing
``seq[len(seq):len(seq)] = iterable``.
.. method:: bytearray.insert(index, value, /)
list.insert(index, value, /)
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.insert(index, value, /)
Insert *value* into *sequence* at the given *index*.
This is equivalent to writing ``sequence[index:index] = [value]``.
.. method:: bytearray.pop(index=-1, /)
list.pop(index=-1, /)
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.pop(index=-1, /)
Retrieve the item at *index* and also removes it from *sequence*.
By default, the last item in *sequence* is removed and returned.
.. method:: bytearray.remove(value, /)
list.remove(value, /)
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.remove(value, /)
Remove the first item from *sequence* where ``sequence[i] == value``.
Raises :exc:`ValueError` if *value* is not found in *sequence*.
.. method:: bytearray.reverse()
list.reverse()
:no-contents-entry:
:no-index-entry:
:no-typesetting:
.. method:: sequence.reverse()
Reverse the items of *sequence* in place.
This method maintains economy of space when reversing a large sequence.
To remind users that it operates by side-effect, it returns ``None``.
.. _typesseq-list:
@@ -5761,9 +5818,10 @@ Methods
.. index:: pair: object; method
Methods are functions that are called using the attribute notation. There are
two flavors: :ref:`built-in methods <builtin-methods>` (such as :meth:`append`
on lists) and :ref:`class instance method <instance-methods>`.
Methods are functions that are called using the attribute notation.
There are two flavors: :ref:`built-in methods <builtin-methods>`
(such as :meth:`~list.append` on lists)
and :ref:`class instance method <instance-methods>`.
Built-in methods are described with the types that support them.
If you access a method (a function defined in a class namespace) through an

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@@ -3142,11 +3142,12 @@ objects. The :mod:`collections.abc` module provides a
:term:`abstract base class` to help create those methods from a base set of
:meth:`~object.__getitem__`, :meth:`~object.__setitem__`,
:meth:`~object.__delitem__`, and :meth:`!keys`.
Mutable sequences should provide methods :meth:`!append`, :meth:`!count`,
:meth:`!index`, :meth:`!extend`, :meth:`!insert`, :meth:`!pop`, :meth:`!remove`,
:meth:`!reverse` and :meth:`!sort`, like Python standard :class:`list`
objects. Finally,
sequence types should implement addition (meaning concatenation) and
Mutable sequences should provide methods :meth:`~sequence.append`,
:meth:`~sequence.count`, :meth:`~sequence.index`, :meth:`~sequence.extend`,
:meth:`~sequence.insert`, :meth:`~sequence.pop`, :meth:`~sequence.remove`,
:meth:`~sequence.reverse` and :meth:`~sequence.sort`,
like Python standard :class:`list` objects.
Finally, sequence types should implement addition (meaning concatenation) and
multiplication (meaning repetition) by defining the methods
:meth:`~object.__add__`, :meth:`~object.__radd__`, :meth:`~object.__iadd__`,
:meth:`~object.__mul__`, :meth:`~object.__rmul__` and :meth:`~object.__imul__`

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@@ -568,7 +568,7 @@ This example, as usual, demonstrates some new Python features:
Different types define different methods. Methods of different types may have
the same name without causing ambiguity. (It is possible to define your own
object types and methods, using *classes*, see :ref:`tut-classes`)
The method :meth:`!append` shown in the example is defined for list objects; it
The method :meth:`~list.append` shown in the example is defined for list objects; it
adds a new element at the end of the list. In this example it is equivalent to
``result = result + [a]``, but more efficient.

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@@ -142,8 +142,8 @@ Using Lists as Stacks
The list methods make it very easy to use a list as a stack, where the last
element added is the first element retrieved ("last-in, first-out"). To add an
item to the top of the stack, use :meth:`!append`. To retrieve an item from the
top of the stack, use :meth:`!pop` without an explicit index. For example::
item to the top of the stack, use :meth:`~list.append`. To retrieve an item from the
top of the stack, use :meth:`~list.pop` without an explicit index. For example::
>>> stack = [3, 4, 5]
>>> stack.append(6)
@@ -340,7 +340,7 @@ The :keyword:`!del` statement
=============================
There is a way to remove an item from a list given its index instead of its
value: the :keyword:`del` statement. This differs from the :meth:`!pop` method
value: the :keyword:`del` statement. This differs from the :meth:`~list.pop` method
which returns a value. The :keyword:`!del` statement can also be used to remove
slices from a list or clear the entire list (which we did earlier by assignment
of an empty list to the slice). For example::
@@ -500,8 +500,8 @@ any immutable type; strings and numbers can always be keys. Tuples can be used
as keys if they contain only strings, numbers, or tuples; if a tuple contains
any mutable object either directly or indirectly, it cannot be used as a key.
You can't use lists as keys, since lists can be modified in place using index
assignments, slice assignments, or methods like :meth:`!append` and
:meth:`!extend`.
assignments, slice assignments, or methods like :meth:`~list.append` and
:meth:`~list.extend`.
It is best to think of a dictionary as a set of *key: value* pairs,
with the requirement that the keys are unique (within one dictionary). A pair of

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@@ -420,7 +420,7 @@ type, i.e. it is possible to change their content::
[1, 8, 27, 64, 125]
You can also add new items at the end of the list, by using
the :meth:`!list.append` *method* (we will see more about methods later)::
the :meth:`list.append` *method* (we will see more about methods later)::
>>> cubes.append(216) # add the cube of 6
>>> cubes.append(7 ** 3) # and the cube of 7

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@@ -656,7 +656,8 @@ break.
The change which will probably break the most code is tightening up the
arguments accepted by some methods. Some methods would take multiple arguments
and treat them as a tuple, particularly various list methods such as
:meth:`!append` and :meth:`!insert`. In earlier versions of Python, if ``L`` is
:meth:`~list.append` and :meth:`~list.insert`.
In earlier versions of Python, if ``L`` is
a list, ``L.append( 1,2 )`` appends the tuple ``(1,2)`` to the list. In Python
2.0 this causes a :exc:`TypeError` exception to be raised, with the message:
'append requires exactly 1 argument; 2 given'. The fix is to simply add an

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@@ -997,9 +997,10 @@ sequence of bytes::
u'\u31ef \u3244'
Byte arrays support most of the methods of string types, such as
:meth:`startswith`/:meth:`endswith`, :meth:`find`/:meth:`rfind`,
and some of the methods of lists, such as :meth:`append`,
:meth:`pop`, and :meth:`reverse`.
:meth:`~bytearray.startswith`/:meth:`~bytearray.endswith`,
:meth:`~bytearray.find`/:meth:`~bytearray.rfind`,
and some of the methods of lists, such as :meth:`~bytearray.append`,
:meth:`~bytearray.pop`, and :meth:`~bytearray.reverse`.
::
@@ -1528,8 +1529,8 @@ Some smaller changes made to the core Python language are:
the :exc:`StopIteration` exception will be raised. (Backported
in :issue:`2719`.)
* Tuples now have :meth:`index` and :meth:`count` methods matching the
list type's :meth:`index` and :meth:`count` methods::
* Tuples now have :meth:`~tuple.index` and :meth:`~tuple.count` methods
matching the list type's :meth:`~list.index` and :meth:`~list.count` methods::
>>> t = (0,1,2,3,4,0,1,2)
>>> t.index(3)

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@@ -1292,7 +1292,7 @@ This section covers specific optimizations independent of the
(Contributed by Stefan Behnel in :gh:`68264`.)
* Resizing lists is streamlined for the common case,
speeding up :meth:`!list.append` by ≈15%
speeding up :meth:`list.append` by ≈15%
and simple :term:`list comprehension`\s by up to 20-30%
(Contributed by Dennis Sweeney in :gh:`91165`.)

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@@ -2176,7 +2176,7 @@ New Features
(Contributed by Sam Gross in :gh:`114329`.)
* Add the :c:func:`PyList_Extend` and :c:func:`PyList_Clear` functions,
mirroring the Python :meth:`!list.extend` and :meth:`!list.clear` methods.
mirroring the Python :meth:`list.extend` and :meth:`list.clear` methods.
(Contributed by Victor Stinner in :gh:`111138`.)
* Add the :c:func:`PyLong_AsInt` function.

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@@ -2380,8 +2380,8 @@ Porting Python code
for top-level modules. E.g. ``__import__('sys', level=1)`` is now an error.
* Because :data:`sys.meta_path` and :data:`sys.path_hooks` now have finders on
them by default, you will most likely want to use :meth:`!list.insert` instead
of :meth:`!list.append` to add to those lists.
them by default, you will most likely want to use :meth:`list.insert` instead
of :meth:`list.append` to add to those lists.
* Because ``None`` is now inserted into :data:`sys.path_importer_cache`, if you
are clearing out entries in the dictionary of paths that do not have a

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@@ -4913,11 +4913,11 @@ Allow tuples of length 20 in the freelist to be reused.
.. nonce: lYKYYP
.. section: Core and Builtins
:exc:`ValueError` messages for :meth:`!list.index`, :meth:`!range.index`,
:exc:`ValueError` messages for :meth:`list.index`, :meth:`range.index`,
:meth:`!deque.index`, :meth:`!deque.remove` and :meth:`!ShareableList.index`
no longer contain the repr of the searched value (which can be arbitrary
large) and are consistent with error messages for other :meth:`!index` and
:meth:`!remove` methods.
large) and are consistent with error messages for other :meth:`~sequence.index` and
:meth:`~sequence.remove` methods.
..
@@ -5604,7 +5604,7 @@ Using :data:`NotImplemented` in a boolean context now raises
.. nonce: wNMKVd
.. section: Core and Builtins
Fix race condition in free-threaded build where :meth:`!list.extend` could
Fix race condition in free-threaded build where :meth:`list.extend` could
expose uninitialised memory to concurrent readers.
..

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@@ -671,7 +671,7 @@ Allow the JIT to remove an extra ``_TO_BOOL_BOOL`` instruction after
.. nonce: dNh64H
.. section: Core and Builtins
Fix crash when calling :meth:`!list.append` as an unbound method.
Fix crash when calling :meth:`list.append` as an unbound method.
..