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, Aug 02 '15 at 02:03

Paul Cornelius · Answer 1 · 2015-07-31T22:42:19.573

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 '15 at 22:42

answered Jul 31 '15 at 21:32

Paul Cornelius

9,245
1
15
24

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. – busymind Aug 01 '15 at 02:14

score 2 · Answer 2 · edited May 23 '17 at 11:51

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 '17 at 11:51

Community

1
1

answered Jul 31 '15 at 21:40

Ewan

14,592
6
48
62

1

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 Jul 31 '15 at 22:48

Pass variable from one class to another Python

2 Answers2