Python Global Variable not updating

Question

I'm new with Python and programming but I can't seem to understand why this function does not update the global variable

global weight
weight = 'value'
def GetLiveWeight():
    SetPort()
    while interupt == False:
        port.write(requestChar2)
        liveRaw = port.read(9)
        liveRaw += port.read(port.inWaiting())
        time.sleep(0.2)
        weight = liveRaw.translate(None, string.letters)
    return weight

I also tried this:

weight = 'value'
def GetLiveWeight():
    global weight
    SetPort()
    while interupt == False:
        port.write(requestChar2)
        liveRaw = port.read(9)
        liveRaw += port.read(port.inWaiting())
        time.sleep(0.2)
        weight = liveRaw.translate(None, string.letters)
    return weight

try:
    threading.Thread(target = GetLiveWeight).start()
    print liveWeight
except:
    print "Error: unable to start thread"

Answer 1

You need to declare that weight is global inside GetLiveWeight, not outside it.

weight = 'value'
def GetLiveWeight():
    global weight

The global statement tells Python that within the scope of the GetLiveWeight function, weight refers to the global variable weight, not some new local variable weight.