[Python-Dev] Patch review [ 1093585 ] sanity check for readline remove/replace

[Michiel Jan Laurens de Hoon]

Patch review [ 1093585 ] sanity check for readline remove/replace

The functions remove_history_item and replace_history_item in the readline
module respectively remove and replace an item in the history of commands. As
outlined in bug [ 1086603 ], both functions cause a segmentation fault if the
item index is negative. This is actually a bug in the corresponding functions in
readline, which return a NULL pointer if the item index is larger than the size
of the history, but does not check for the item index being negative. I sent a
patch to bug-readline at gnu.org, so this will probably be fixed in future versions
of readline. But for now, we need a workaround in Python.

The patched code checks if the item index is negative, and issues an error
message if so. I have run the test suite after applying this patch, and I
found no problems with it.

Note that there is one more way to fix this bug, which is to interpret negative
indeces as counting from the end (same as lists and strings for exampe). So 
remove_history_item(-1) removes the last item added to the history etc. In that 
case, get_history_item should change as well. Right now get_history_item(-1) 
returns None, so the patch introduces a small (and probably insignificant) 
inconsistency: get_history_item(-1) returns None but remove_history_item(-1) 
raises an error.

--Michiel.


-- 
Michiel de Hoon, Assistant Professor
University of Tokyo, Institute of Medical Science
Human Genome Center
4-6-1 Shirokane-dai, Minato-ku
Tokyo 108-8639
Japan
http://bonsai.ims.u-tokyo.ac.jp/~mdehoon