CODEWITHSUNDEEP
pythonmultithreading
Ryan
Ryan

Reputation: 12113

can someone help me understand this short .py

I'm trying to understand basic threading in python, I'm having trouble understanding how pooling works with the queue module. Heres the example server used in the howto I'm reading from: http://www.devshed.com/c/a/Python/Basic-Threading-in-Python/2/. Basically what I don't understand is how the variable pickledList ends up available to the threads scope to be shipped out to the client since its never passed to the thread anywhere in the code

import pickle
import Queue
import socket
import threading

# We'll pickle a list of numbers, yet again:
someList = [ 1, 2, 7, 9, 0 ]
pickledList = pickle.dumps ( someList )

# A revised version of our thread class:
class ClientThread ( threading.Thread ):

   # Note that we do not override Thread's __init__ method.
   # The Queue module makes this not necessary.

   def run ( self ):

      # Have our thread serve "forever":
      while True:

         # Get a client out of the queue
         client = clientPool.get()

         # Check if we actually have an actual client in the client variable:
         if client != None:

            print 'Received connection:', client [ 1 ] [ 0 ]
            client [ 0 ].send ( pickledList )
            for x in xrange ( 10 ):
               print client [ 0 ].recv ( 1024 )
            client [ 0 ].close()
            print 'Closed connection:', client [ 1 ] [ 0 ]

# Create our Queue:
clientPool = Queue.Queue ( 0 )

# Start two threads:
for x in xrange ( 2 ):
   ClientThread().start()

# Set up the server:
server = socket.socket ( socket.AF_INET, socket.SOCK_STREAM )
server.bind ( ( '', 2727 ) )
server.listen ( 5 )

# Have the server serve "forever":
while True:
   clientPool.put ( server.accept() )

Upvotes: 2

Views: 272

Answers (2)

Christopher
Christopher

Reputation: 9084

Threads don't have their own namespace. pickledList is defined as a global, so it is accessible to the object. Technically it should have had a global pickledList at the top of the function to make that clear, but it's not always needed.

EDIT

By make it clear, I mean "make it clear to a human."

Upvotes: -2

Ville Laurikari
Ville Laurikari

Reputation: 29258

The pickledList variable is available as a global variable in the ClientThread class. See Short Description of Python Scoping Rules.

Upvotes: 4

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