Python Tutorial on Multithreading


K

KevinSimonson

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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A

Alexander Kapps

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.

That tutorial seems to be wrong.

According to the official docs:

"If the subclass overrides the constructor, it must make sure to
invoke the base class constructor (Thread.__init__()) before doing
anything else to the thread."

http://docs.python.org/library/threading.html#thread-objects

So, change your __init__ to this:

class myThread (threading.Thread):
def __init__(self, threadID, name, q):
threading.Thread.__init__(self)
self.threadID = threadID
self.name = name
self.q = q


HTH
 
K

KevinSimonson

That tutorial seems to be wrong.

According to the official docs:

"If the subclass overrides the constructor, it must make sure to
invoke the base class constructor (Thread.__init__()) before doing
anything else to the thread."

http://docs.python.org/library/threading.html#thread-objects

So, change your __init__ to this:

class myThread (threading.Thread):
     def __init__(self, threadID, name, q):
         threading.Thread.__init__(self)
         self.threadID = threadID
         self.name = name
         self.q = q

Alexander, thanks! Your suggestion fixed my problem.

Kevin S
 
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