Holding until next value change

[Arshpreet Singh]

I am writing a function as main_call() which is continuously producing values. 
(+ve or -ve) I want to print on screen only for first +ve value and hold until 
-ve value comes around. here is my code:


def main_call():
    while True:
        yield strategy()
 
for value in main_call():
    if(value>0):
        print '+ve'
    elif(value>0):
        print '-ve'
    else:
        pass 

Do I need to use threads or processes?
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