Python Tutorial on Multithreading

KevinSimonson kvnsmnsn at hotmail.com
Mon Feb 21 23:30:26 CET 2011


I've been teaching myself Python from the tutorial routed at "http://
www.tutorialspoint.com/python/index.htm".  It's worked out pretty
well, but when I copied its multithreading example from the bottom of
the page at "http://www.tutorialspoint.com/python/
python_multithreading.htm" and tried to run it I got the error
messages:

C:\Users\kvnsmnsn\Python>python mt.py
Traceback (most recent call last):
  File "mt.py", line 38, in <module>
    thread = myThread(threadID, tName, workQueue)
  File "mt.py", line 10, in __init__
    self.name = name
  File "C:\Python27\lib\threading.py", line 667, in name
    assert self.__initialized, "Thread.__init__() not called"
AssertionError: Thread.__init__() not called

I don't really understand why it's giving me these messages.
<__initialized> gets set to <True> when <__init__()> gets called.
Granted my Python program calls <__init__()> with only one parameter,
and the constructor in "threading.py" takes _seven_ parameters, but
all but one have default values, so a call with just one parameter
should be legal.  Why then is <__initialized> getting set to <True>?

My code follows.

Kevin Simonson

import Queue
import threading
import time

exitFlag = 0

class myThread (threading.Thread):
    def __init__(self, threadID, name, q):
        self.threadID = threadID
        self.name = name
        self.q = q
        threading.Thread.__init__(self)
    def run(self):
        print "Starting " + self.name
        process_data(self.name, self.q)
        print "Exiting " + self.name

def process_data(threadName, q):
    while not exitFlag:
        queueLock.acquire()
        if not workQueue.empty():
            data = q.get()
            queueLock.release()
            print "%s processing %s" % (threadName, data)
        else:
            queueLock.release()
        time.sleep(1)

threadList = ["Thread-1", "Thread-2", "Thread-3"]
nameList = ["One", "Two", "Three", "Four", "Five"]
queueLock = threading.Lock()
workQueue = Queue.Queue(10)
threads = []
threadID = 1

# Create new threads
for tName in threadList:
    thread = myThread(threadID, tName, workQueue)
    thread.start()
    threads.append(thread)
    threadID += 1

# Fill the queue
queueLock.acquire()
for word in nameList:
    workQueue.put(word)
queueLock.release()

# Wait for queue to empty
while not workQueue.empty():
    pass

# Notify threads it's time to exit
exitFlag = 1

# Wait for all threads to complete
for t in threads:
    t.join()
print "Exiting Main Thread"



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