bpo-38843: Document behavior of default when the attribute is already set (GH-23653) (#23668)

(cherry picked from commit 752cdf21eb2be0a26ea6a34a0de33a458459aead)

Co-authored-by: Raymond Hettinger <rhettinger@users.noreply.github.com>

Co-authored-by: Raymond Hettinger <rhettinger@users.noreply.github.com>
1 file changed