I get a random TypeError exception thrown whenever I interrupt/kill a sleeping parent thread from a child thread but ONLY if the python script was invoked by a shell script with an & argument to make it run in the background. (this is in vanilla python)

This doesn't happen if invoked 

(1) in command line
(2) in command line with &
(3) in shell script (without &)

Only in shell script with &.

Here is the python script named psc.py https://pastebin.com/raw/KZQptCMr
And here is the shell script named ssc.sh https://pastebin.com/raw/QQzs4Tpz that when ran will run the python script and cause the strange behaviour

Here is the output I'm seeing: -------------------
parent looping
child interrupting parent
why would I ever catch a TypeError?
Traceback (most recent call last):
  File "m.py", line 17, in <module>
    time.sleep(1)
TypeError: 'int' object is not callable

Here is the output I'm expecting: --------------------
parent looping
child interrupting parent
caught interruption raised from user or child thread :)

Another unexpected behaviour might be that python suddenly hangs.

Here is a stackoverflow question raised on this issue with discussion in the comments https://stackoverflow.com/questions/65440353/python-time-sleep1-raises-typeerror?noredirect=1#comment115697237_65440353