Invalid syntax when there is add operation in the listener

Css generates python code with invalid syntax when there is an addition operation in the listener.
Here is my listener:
self.song().tracks[self.get_modifier_value("m3")].clip_slots[self.get_modifier_value("m4") + 1].clip.add_playing_status_listener

which generates the following function name in .py file:
def _mode1_self_song_tracks_self_get_modifier_value__m3__clip_slots_self_get_modifier_value__m4__+_1_clip_add_playing_status_listener_id_22(self):

Because of the plus sign (+) in the name the script will not compile and not show up in Ableton's control surface menu.
The only workaround I'm aware of is to manually remove the plus sign from the .py file. Then it works without problems.

Could this be fixed?