Generators can be used to implement coroutines:
# create and advance generator to the first yield
def coroutine(func):
def start(*args,**kwargs):
cr = func(*args,**kwargs)
next(cr)
return cr
return start
# example coroutine
@coroutine
def adder(sum = 0):
while True:
x = yield sum
sum += x
# example use
s = adder()
s.send(1) # 1
s.send(2) # 3
Coroutines are commonly used to implement state machines, as they are primarily useful for creating single-method procedures that require a state to function properly. They operate on an existing state and return the value obtained on completion of the operation.