bpo-35838: document optionxform must be idempotent (GH-12656)

(cherry picked from commit 04694a3) Co-authored-by: Inada Naoki <songofacandy@gmail.com>
python · Apr 2, 2019 · 9a838c5 · 9a838c5
1 parent 5ca4fe0
commit 9a838c5
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/Doc/library/configparser.rst b/Doc/library/configparser.rst
@@ -723,6 +723,12 @@ be overridden by subclasses or by attribute assignment.
      >>> list(custom['Section2'].keys())
      ['AnotherKey']
 
+  .. note::
+     The optionxform function transforms option names to a canonical form.
+     This should be an idempotent function: if the name is already in
+     canonical form, it should be returned unchanged.
+
+
 .. attribute:: ConfigParser.SECTCRE
 
   A compiled regular expression used to parse section headers.  The default