Local variable '…' referenced before assignment

Question

I'm new with Python and I've encountered this error this afternoon. I tried to fix this by adding global before the previous variable but I continue to get this error:

Traceback (most recent call last):
  File "send.py", line 76, in <module>
main(sys.argv[1:])
  File "send.py", line 34, in main
send()
  File "send.py", line 29, in send
    if data != previous:

A sample of the code I did:

import socket
import sys
import getopt
import time
import threading

sys.path.insert(0, '/usr/lib/python2.7/bridge/') 

from bridgeclient import BridgeClient as bridgeclient

def main(argv):
    global bridge
    global previous

    try:                    
        # Create a UDP socket.
        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        server_address = ('192.168.1.100', 9050)

        bridge = bridgeclient()
        previous = ""

        # Send data  
        def send():         
            data = bridge.get("data")   

            if data != previous:                    
                sent = sock.sendto(data, server_address)                                
                previous = data
                threading.Timer(0.2, send).start()

        send()

    finally:
        sock.close()

if __name__ == "__main__":
    main(sys.argv[1:])

Answer 1

You have nested scopes here:

def main(argv):
    ...
    global previous
    ...
    def send():
        ...
        if data != previous:

Declaring global in main function does not apply to the local in send function.

You could move the global declaration for the previous into the start of the send method. You can remove the global declaration for bridge completely.

Better yet, refactor your code not to use nested scopes and global variables!