A test program to show some oddity's of multiprocessing.pool behavior.

pool_test.py

#************ WARNING, this script can create rouge python instances that need to be manually killed. **************
from Tkinter import *
from multiprocessing import Pool
import time

def myfunc(x):
##    window = Tk() # Adding this code causes a crash (loudly and I can not explain.)
##    lbl = Label(window, text="Thread %d" % x)
##    lbl.grid(column=0, row=0)
##    window.mainloop()
    time.sleep(1)
    return x*x

window = Tk()
lbl = Label(window, text="Main")
lbl.grid(column=0, row=0)
window.mainloop()
pool = Pool(processes = 4) #Crashes here in IDLE
resultlist = pool.map(myfunc, range(10))
pool.close()
print(resultlist)

pool_test_output.txt

#************ WARNING, this script can create rouge python instances that need to be manually killed. **************
MacOSX:Desktop user$ python2 -V
Python 2.7.15
MacOSX:Desktop user$ python2 -i pool_test.py 
Main
Created main process, press the 'X' to continue.
'X' pressed continuing...
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
>>> exit()
MacOSX:Desktop user$ python2
Python 2.7.15 (default, Jun 17 2018, 12:46:58) 
[GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pool_test
Main
Created main process, press the 'X' to continue.
'X' pressed continuing...
^CProcess PoolWorker-2:
Process PoolWorker-4:
Process PoolWorker-3:
Traceback (most recent call last):
Traceback (most recent call last):
Process PoolWorker-1:
Traceback (most recent call last):
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 267, in _bootstrap
Traceback (most recent call last):
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 267, in _bootstrap
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 267, in _bootstrap
    self.run()
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 114, in run
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 267, in _bootstrap
    self.run()
    self.run()
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 114, in run
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
    self._target(*self._args, **self._kwargs)
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/pool.py", line 102, in worker
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/pool.py", line 102, in worker
    task = get()
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/queues.py", line 376, in get
    task = get()
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/queues.py", line 374, in get
    return recv()
    racquire()
KeyboardInterrupt
KeyboardInterrupt
    self._target(*self._args, **self._kwargs)
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/pool.py", line 102, in worker
    task = get()
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/queues.py", line 374, in get
    self.run()
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/process.py", line 114, in run
    racquire()
    self._target(*self._args, **self._kwargs)
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/pool.py", line 102, in worker
KeyboardInterrupt
    task = get()
  File "/usr/local/Cellar/python@2/2.7.15_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/multiprocessing/queues.py", line 374, in get
    racquire()
KeyboardInterrupt
^Z
[1]+  Stopped                 python2
MacOSX:Desktop user$