[Python-checkins] bpo-33609: Document dict insertion order guarantee as of 3.7 (GH-7093)
Ned Deily
webhook-mailer at python.org
Mon Jun 4 18:09:33 EDT 2018
https://github.com/python/cpython/commit/f822549653d8d09bffff5b7dcddfdf12679a787c
commit: f822549653d8d09bffff5b7dcddfdf12679a787c
branch: master
author: INADA Naoki <methane at users.noreply.github.com>
committer: Ned Deily <nad at python.org>
date: 2018-06-04T18:09:22-04:00
summary:
bpo-33609: Document dict insertion order guarantee as of 3.7 (GH-7093)
files:
M Doc/library/stdtypes.rst
diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index af2b4e1cb66a..80dfe88cc58c 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -4248,6 +4248,29 @@ pairs within braces, for example: ``{'jack': 4098, 'sjoerd': 4127}`` or ``{4098:
value)`` pairs. Order comparisons ('<', '<=', '>=', '>') raise
:exc:`TypeError`.
+ Dict preserves insertion order. Note that updating key doesn't affects the
+ order. On the other hand, keys added after deletion are inserted to the
+ last. ::
+
+ >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
+ >>> d
+ {'one': 1, 'two': 2, 'three': 3, 'four': 4}
+ >>> list(d)
+ ['one', 'two', 'three', 'four']
+ >>> list(d.values())
+ [1, 2, 3, 4]
+ >>> d["one"] = 42
+ >>> d
+ {'one': 42, 'two': 2, 'three': 3, 'four': 4}
+ >>> del d["two"]
+ >>> d["two"] = None
+ >>> d
+ {'one': 42, 'three': 3, 'four': 4, 'two': None}
+
+ .. versionchanged:: 3.7
+ Dict order is guaranteed to be insertion order. This behavior was
+ implementation detail of CPython from 3.6.
+
.. seealso::
:class:`types.MappingProxyType` can be used to create a read-only view
of a :class:`dict`.
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