- def genny(): 
-     yield 1 
-     yield 2 
-     yield 3 
-   
- def middleman(input_gen=None): 
- 	return genny() if input_gen is None else input_gen 
-   
- if __name__ == '__main__': 
-     pro = middleman() 
-     for e in pro: 
-     	pro = middleman(pro) 
-     	print e 
-   
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