Using a global variable with a thread

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You just need to declare a as a global in thread2, so that you aren’t modifying an a that is local to that function.

def thread2(threadname):
    global a
    while True:
        a += 1
        time.sleep(1)

In thread1, you don’t need to do anything special, as long as you don’t try to modify the value of a (which would create a local variable that shadows the global one; use global a if you need to)>

def thread1(threadname):
    #global a       # Optional if you treat a as read-only
    while a < 10:
        print a

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