Python IDLE compatible with multithreading?

Question

It seems that IDLE (part of the standard Python Windows install) will not execute multithreaded programs correctly without nasty hangs or bugout crashes. Does anyone know of a way to fix this?

The following program will always hang in IDLE but complete normally when executed with the Python interpreter directly:

import threading, time

printLock = threading.Lock()

def pl(s):
  printLock.acquire()
  print s
  printLock.release()

class myThread( threading.Thread ):
  def run(self):
    i = 0
    for i in range(0,30):
      pl(i)
      time.sleep(0.1)

t = myThread()
t.start()

while threading.activeCount() > 1:
  time.sleep(1)
  pl( time.time() )

print "all done!"

sample output:

U:\dev\py\multithreadtest>python mt.py
0
1
2
3
4
5
6
7
8
9
1277935368.84
10
11
12
13
14
15
16
17
18
19
1277935369.84
20
21
22
23
24
25
26
27
28
29
1277935370.84
1277935371.84
all done!

output when using IDLE "Run Module" function always hangs indefinitely at around the time the line reading 23 or 24 shows up on my machine.

Answer 1

import threading
print(threading.activeCount())

prints 1 when run at the command line, 2 when run from Idle. So your loop

while threading.activeCount() > 1:
  time.sleep(1)
  pl( time.time() )

will terminate in the console but continue forever in Idle.

To fix the problem in the posted code, add something like

initial_threads = threading.activeCount()

after the import and change the loop header to

while threading.activeCount() > initial_threads:

With this change, the code runs through 30 cycles and stops with 'all done!'. I have added this to my list of console Python versus Idle differences that need to be documented.