From 6bd058e0ff5d4a63fb35f6d45161cdf51cb68c58 Mon Sep 17 00:00:00 2001 From: "Miss Skeleton (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Sun, 4 Oct 2020 16:23:43 -0700 Subject: [PATCH] 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 --- Doc/library/xml.etree.elementtree.rst | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst index 44ac52aa830..e4aedd1f9f0 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