Python socket issue with Tkinter

sharkDawg

Hi guys, im currently doing a robotics project in college, its a robot that has to be controlled from a pc over a wireless LAN connection. All was going well until i got to the server - client stage. I am using python to code these and can get a connection between them but cannot send characters from the client to the server. I haven't used python before so i may well have made some basic errors.

Heres what i have:

#!/usr/bin/env python

from Tkinter import *
import socket
import sys
import tkMessageBox

def ifup():
   testConn = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
   try:
    host = 'localhost'
    port = 50002
    size = 1024
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((host,port))
    tkMessageBox.showinfo('Connection Box',' Yes connected ')
   except:
    tkMessageBox.showinfo('Connection Box',' Not connected ')



def forward(event):
    s.send('<Key-w>')

def reverse(event):
    s.send('<Key-s>')

def left(event):
    s.send('<Key-a>')
    
def right(event):
    s.send('<Key-d>')

def quit(event):
    s.send('<Key-Escape>')
    s.close()    
    sys.exit()

ifup()

tkroot = Tk()
labelfont = ('courier',20,'bold')
widget = Label(tkroot, text='I love Robotics!')
widget.config(bg='yellow', font = labelfont)
widget.config(height=5, width=20)
widget.pack(expand=YES, fill = BOTH)
widget.bind('<Key-w>',forward)
widget.bind('<Key-a>',left)
widget.bind('<Key-d>',right)
widget.bind('<Key-s>',reverse)
widget.bind('<Key-Escape>',quit)
widget.focus()
tkroot.mainloop()

When I press any of the defined key's, i get an error like this

Exception in Tkinter callback
Traceback (most recent call last):
  File "lib-tk/Tkinter.py", line 1406, in __call__
    return self.func(*args)
  File "/home/enda/test.py", line 23, in forward
    s.send('<Key-w>')
NameError: global name 's' is not defined

Is there something fundamental i'm doing wrong? Any help would be greatfully appreciated

sobriquet

sharkDawg wrote: »

Is there something fundamental i'm doing wrong?

Yep, it's a simple scoping issue: you declare 's' in ifup, and when that method ends, it goes out of scope. So in the method 'forward', you declare use 's' even though the interpreter has no idea what 's' is supposed to be.

So you need to modify the scope of 's'. The best option might be to wrap up the ifup and forward (etc) methods you have into a class, have 's' as a class variable/property, and have forward/reverse etc stubs to wrap the appropriate class methods and to bind to the Tkinter widgets. (It might be possible to bind the widget to class.method directly, I'm not sure.)

If you're not used Python, the issue doesn't come up until you run the 'forward' because it's dynamic - the expression 's.send(...)' isn't evaluated at all until the interpreter hits it. If you're used to Java, C# etc, you'd expect such a thing to be caught at compile time.

sharkDawg

Cheers man, thanks, it's quite obvious really, have it sorted now.