gh-48181: Document codecs.charmap_build (#135997)

StanFromIreland · web-flow · commit 2bdd50309f54 · 2025-06-30T15:42:08.000+02:00
diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
@@ -53,6 +53,14 @@ any codec:
    :exc:`UnicodeDecodeError`). Refer to :ref:`codec-base-classes` for more
    information on codec error handling.
 
+.. function:: charmap_build(string)
+
+   Return a mapping suitable for encoding with a custom single-byte encoding.
+   Given a :class:`str` *string* of up to 256 characters representing a
+   decoding table, returns either a compact internal mapping object
+   ``EncodingMap`` or a :class:`dictionary <dict>` mapping character ordinals
+   to byte values. Raises a :exc:`TypeError` on invalid input.
+
 The full details for each codec can also be looked up directly:
 
 .. function:: lookup(encoding, /)
