From: Miss Skeleton (bot) <31488909+miss-islington@users.noreply.github.com>
Date: Sun, 4 Oct 2020 23:56:56 +0000 (-0700)
Subject: bpo-41892: Clarify that an example in the ElementTree docs explicitly avoids modifyin... 
X-Git-Tag: v3.9.1rc1~200
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d5719247ba32b3ac700454bad9a9e2cc7edeac6a;p=thirdparty%2FPython%2Fcpython.git

bpo-41892: Clarify that an example in the ElementTree docs explicitly avoids modifying an XML tree while iterating over it. (GH-22464) (GH-22554)

(cherry picked from commit 40db798692ca783fc2163656f196ac77e8b9e792)

Co-authored-by: scoder <stefan_ml@behnel.de>

Co-authored-by: scoder <stefan_ml@behnel.de>
---

diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst
index 7725e4d158d4..f4bccf660981 100644
--- a/Doc/library/xml.etree.elementtree.rst
+++ b/Doc/library/xml.etree.elementtree.rst
@@ -251,12 +251,18 @@ We can remove elements using :meth:`Element.remove`.  Let's say we want to
 remove all countries with a rank higher than 50::
 
    >>> for country in root.findall('country'):
+   ...     # using root.findall() to avoid removal during traversal
    ...     rank = int(country.find('rank').text)
    ...     if rank > 50:
    ...         root.remove(country)
    ...
    >>> tree.write('output.xml')
 
+Note that concurrent modification while iterating can lead to problems,
+just like when iterating and modifying Python lists or dicts.
+Therefore, the example first collects all matching elements with
+``root.findall()``, and only then iterates over the list of matches.
+
 Our XML now looks like this:
 
 .. code-block:: xml