flow control / get next / filter?

[Ken Godee]

I'm trying to figure out how to get the value of a variable
that's constantly getting updated, but only get the new
value, once it has changed.

I have a module where I register a call back to a function
in the code I'm working on. This function gets updated continuely.
ie....

x = ''
def myfunc(event)
     global x
     x = event

if you where to do a while loop, you would end up with something like...

while 1:
     print x
     if x == 'stop':
         break

1,1,1,1,1,1,2,2,2,2,2,3,3,3,3,3,

if you where to do a nested while, you would get....

while 1:
     print x
     while x != x:
         print x
         if x == 'stop':
             break
     if x == 'stop':
         break

1,2,3,4,5

but it of coarse just spins the loop and processor loads pegs out.

If someone could point me in a direction, I'd appreciate it.
Thanks