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

Miss Skeleton (bot) webhook-mailer at python.org
Sun Oct 4 19:23:52 EDT 2020


https://github.com/python/cpython/commit/6bd058e0ff5d4a63fb35f6d45161cdf51cb68c58
commit: 6bd058e0ff5d4a63fb35f6d45161cdf51cb68c58
branch: 3.8
author: Miss Skeleton (bot) <31488909+miss-islington at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2020-10-04T16:23:43-07:00
summary:

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

(cherry picked from commit 40db798692ca783fc2163656f196ac77e8b9e792)

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

files:
M Doc/library/xml.etree.elementtree.rst

diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst
index 44ac52aa83079..e4aedd1f9f082 100644
--- a/Doc/library/xml.etree.elementtree.rst
+++ b/Doc/library/xml.etree.elementtree.rst
@@ -249,12 +249,18 @@ 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



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