You can clone with
If there is a regular str object with non-ascii characers in a doc string. Then the kernel crashes when showing a tooltip for that object. Using master ee9e1d9.
Example run the script in https://gist.github.com/1198484
typing a( at a prompt will show the tooltip
typing b( at a prompt will crash the kernel
jsonutil.json_clean() inappropriately treats basestring as safe, when bytes objects are most certainly not safe. Should be a tiny fix.
Fixed by PR #769
Don't treat bytes objects as json-safe