python generator
# A generator-function is defined like a normal function, # but whenever it needs to generate a value, # it does so with the yield keyword rather than return. # If the body of a def contains yield, # the function automatically becomes a generator function. # Python 3 example def grepper_gen(): yield "add" yield "grepper" yield "answer" grepper = grepper_gen() next(grepper) > add next(grepper) > grepper next(grepper) > answer