I do not think that readline-cancel.patch is sufficient. The clean up function that readline uses internally (http://git.savannah.gnu.org/cgit/readline.git/tree/isearch.c#n720 ) also cleans up the context that used by isearch.

The functions to cleanup the context (and a pointer to the context) are exposed on `rlprivate.h` so python _can_ get at them to support old versions of rl. Once started down that path for isearch mode, might as well vendor all of rl_callback_sigcleanup() which will end up being 50-100 LoC (some of the helper functions will also need to be vendored).