If an unhandled exception occurs in idle_add/timeout_add the source doesn't get removed, leading to endless calls of the same function which leads to the same exception again... 

While this is of course a user error, it is really hard to debug errors since stdout/stderr get spamed without end.

Possible solutions I can imagine:
 - Handle in the overrides, print the stacktrace and return False
 - Somehow make the bool return value in case of an error False in all callbacks..

The following example leads to endless stacktraces, while only one is printed with pygtk.

##################################

from gi.repository import GLib, Gtk
def faulty_function():
    raise Exception
GLib.idle_add(faulty_function)
Gtk.main()