From: Raymond Hettinger <rhettinger@users.noreply.github.com>
Date: Sun, 28 Apr 2019 07:22:36 +0000 (-0700)
Subject: bpo-36715: Add usage note for dict.fromkeys() (GH-12974)
X-Git-Tag: v3.8.0a4~79
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=da63b321f63b697f75e7ab2f88f55d907f56c187;p=python

bpo-36715: Add usage note for dict.fromkeys() (GH-12974)
---

diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index aeecdbb24a..0a6bb14907 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -4254,7 +4254,10 @@ pairs within braces, for example: ``{'jack': 4098, 'sjoerd': 4127}`` or ``{4098:
       Create a new dictionary with keys from *iterable* and values set to *value*.
 
       :meth:`fromkeys` is a class method that returns a new dictionary. *value*
-      defaults to ``None``.
+      defaults to ``None``.  All of the values refer to just a single instance,
+      so it generally doesn't make sense for *value* to be a mutable object
+      such as an empty list.  To get distinct values, use a :ref:`dict
+      comprehension <dict>` instead.
 
    .. method:: get(key[, default])