bpo-41892: Clarify that an example in the ElementTree docs explicitly avoids modifying an XML tree while iterating over it. (GH-22464)
diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst
index 7725e4d..f4bccf6 100644
--- a/Doc/library/xml.etree.elementtree.rst
+++ b/Doc/library/xml.etree.elementtree.rst
@@ -251,12 +251,18 @@
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