Question

is this correct way of doing.i am a newbie python

class main(threading.Thread):
    queueLock = threading.Lock()
    EppQueue = Queue.Queue(1)
    CrQueue = Queue.Queue(1)
    EPP = threading.Thread(name='EPP', target=EPP, args=(0,EppQueue,))
    cr = threading.Thread(name='cr', target=CR, args=(0,CrQueue,))
    EPP.setDaemon(True)
    EPP.start()
    Cr.start()
    self.send_queue("EppQueue","sss")
    self.send_queue("CrQueue","ssds")

    def send_queue(self,queuename,qvalue,b=None):
        if b is None:
            b = self.queuename
        self.queueLock.acquire()
        self.b.put(qvalue)
        self.queueLock.release()

when i run this i get NameError: name ‘self’ is not defined ???

Answer 1

The variable self (the first argument to a class method – you can use any name for it) is meant to refer to a class instance (also called an object). You use self where self is not defined, right out in the class where no specific object is yet known.

When the code queueLock = threading.lock() … etc, is executed you are not in a class object (instance) but in the context of the class, so your lock will be the same for all objects of the class.

About send_queue, it’s defined and known to all objects via the class, so you do not need to use self. to access it.

If you want some code to be executed at instance creation put it in __init__.

class main(threading.Thread):
  def __init__(self):
    self.queueLock = threading.Lock() 
    .. some code ... 
    send_queue("EppQueue","sss")
    send_queue("CrQueue","ssds")