Python threading issue, raw_input() blocks thread, runaway thread

Question

I'm having an issue with threading in python, the issue seems to be that when I call a thread subsequently calling raw_input() blocks the thread. Here is the minimal example

import threading
import time

class tread_test(threading.Thread):
    def __init__(self):
        self.running = True
        threading.Thread.__init__(self)
    #

    def run(self):
        self.foo()
    #

    def foo(self):
        print "Spam, Spam, Spam"
        self.task = threading.Timer(0.5, self.foo)
        self.task.start()
    #

    def stop(self):
        self.running = False
        self.task.cancel()
    #
#

if __name__ == "__main__":
    a = tread_test()
    print "Starting now"
    a.start()
    raw_input()
    a.stop()
    print "Stopping now"

What I expect from this is:

Starting now
Spam, Spam, Spam
Spam, Spam, Spam
Spam, Spam, Spam
** user hits enter **
Stopping now

Here is what this gives me:

>>> 
Starting now
Spam, Spam, Spam

** After several seconds user hits enter **

Traceback (most recent call last):
  File "C:\file\test.py", line 37, in <module>
    a.stop()
  File "C:\file\test.py", line 28, in stop
    self.task.cancel()
AttributeError: 'tread_test' object has no attribute 'task'
>>> Spam, Spam, Spam
Spam, Spam, Spam
Spam, Spam, Spam
Spam, Spam, Spam
Spam, Spam, Spam
Spam, Spam, Spam
Spam, Spam, Spam
================================ RESTART ================================

Where it keeps printing out until I restart the terminal. When I replace the raw_input() command with threading.sleep() to pause for some amount of time it works as expected. It seems to me that raw_input() is somehow blocking the Timer in foo() from executing.

Why isn't this working as I expect? Is it supposed to work like this for some reason, or am I missing something?

Any help would be appreciated. Thanks!

Hmm, it's working fine for me on both Windows and Linux. What environment are you trying to run the script in? — dano
– dano, Commented Aug 6, 2014 at 19:41
I tried it in a standard python shell in windows and it works as expected. It would seem that the bug is specific to IDLE. — trvrrp
– trvrrp, Commented Aug 6, 2014 at 20:20

dano · Accepted Answer · 2014-08-06 20:26:25Z

5

Your code looks fine, and works for me on both Linux and Windows. I think you're running into a limitation of IDLE's interpreter, which tends to have issues with both multiprocessing and threading-based code. I would simply recommend not trying to run your code from within IDLE.

answered Aug 6, 2014 at 20:26

dano

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