Pass variable from one class to another Python

Question

I managed to create 2 classes that run independently in Python. I want to pass the data variable received from the class DataCom() to tkinter cf_label on the second class.

Is this a correct way to start? I understand that I have to make some variable public in some way but I cannot figure it out. Could someone please help?

from Tkinter import *
import socket
import sys
import time
import datetime
from threading import Thread

def get_constants(prefix):
    """Create a dictionary mapping socket module constants to their names."""
    return dict( (getattr(socket, n), n)
                 for n in dir(socket)
                 if n.startswith(prefix)
                 )


class Example(Frame):

    def __init__(self, parent):
        Frame.__init__(self, parent)   
        self.friend_check = IntVar()
        self.parent = parent
        self.initUI()

    def initUI(self):      
        self.parent.title("Home.local")


        self.cl_label=Label(text="data from socket")
        self.cl_label.grid(row=0,column=0,columnspan=2)



class DataCom(Thread):
    def __init__(self, val):
        Thread.__init__(self)
        self.val = val
    def run(self):
        families = get_constants('AF_')
        types = get_constants('SOCK_')
        protocols = get_constants('IPPROTO_')

        # Create a TCP/IP socket
        sock = socket.create_connection(('localhost', 10000))

        while True:
            try:

                message = 'INFO'

                print >>sys.stderr, 'sending "%s" Length: %s' % (message,len(message))

                sock.sendall(message)

                amount_received = 0
                amount_expected = len(message)

                while amount_received < amount_expected:
                    data = sock.recv(1024)
                    amount_received += len(data)
                    if len(data) != 0:
                        print >>sys.stderr, 'Server received %s %s:Length %s' % (data, len(data))
                    else:
                        sock.close()
                        print >>sys.stderr, 'No more data, closing socket'
                        break
                if not data:
                        break

            finally:

                time.sleep(1)

def main():

    myThread1 = DataCom(4)
    myThread1.setName('Thread 1') 
    myThread1.start()

    root = Tk()

    root.geometry("600x450+900+300")
    root.resizable(0,0)
    app = Example(root)
    root.mainloop()  


if __name__ == '__main__':
    main()

I still not understand how can I pass data from DataCom.data to tkinter label Example Frame. — busymind
– busymind, Commented Aug 2, 2015 at 2:03

Community · Accepted Answer · 2017-05-23 11:51:23Z

2

If you're using threads try using a Queue to share data between threads.

The other option is to declare your variable in class DataCom() as global but be warned, this can cause a lot of confusion and bugs.

A couple of great StackOverflow questions and answers on the subject:

edited May 23, 2017 at 11:51

CommunityBot

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answered Jul 31, 2015 at 21:40

Ewan

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1 Comment

Paul Cornelius Over a year ago

Queues are useful if you want to synchronize the activity of multiple threads. They are unnecessary if all you want to do is share data, since all Python variables occupy the same address space (unless you are using multiple processes, which is not the case here). There is no need for a global variable that I can see.

Paul Cornelius · Accepted Answer · 2015-07-31 22:42:19Z

2

You don't need a public variable, you just need to pass myThread1 as a second parameter to the Example constructor. Then modify Example.__init__ to assign the new argument to a member variable, say theThread. Now all the code in Example can access DataCom.data as self.theThread.data.

edited Jul 31, 2015 at 22:42

answered Jul 31, 2015 at 21:32

Paul Cornelius

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1 Comment

busymind Over a year ago

I thought it was easy but it looks like I will sit tonight to read more about until I will understand this new notions. Appreciate your help. Python is nice.

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