This makes sense, since by definition the generator hasn't gotten to the first yield statement yet, so if we sent a real value there would be nothing to "receive" it. import random def cf(): while True: val = yield print val, def pf(c): while True: val = random.randint(1,10) c.send(val) yield if __name__ == '__main__': c = cf() c.send(None) p = pf(c) for wow in range(10): next(p) Now we can see the function cf() is returning a generator because of the yield keyword. Where is it getting that value from? To use the send method, the generator must wait for a yield statement so that the data sent can be processed or assigned to the variable on the left. When the caller executes R = m.send(a), it puts the object a into the generator's input slot, transfers control to the generator, and waits for a response. There’s also an async version, although this one has to be awaited. 先看一段普通的计算斐波那契续列的代码： 基本版： def old_fib(n): res =  * n index = 0 a = 0 b = 1 while index statement can be used inside the body of a generator. When you're using send to "start" a generator (that is, execute the code from the first line of the generator function up to the first yield statement), you must send None. Post Tags. In Python, yield is the keyword that works similarly as the return statement does in any program by returning the values from the function called. When send() is called to start the generator, it must be called with None as the argument, because there is no yield expression that could receive the value. Return sends a specified value back to its caller whereas Yield can produce a sequence of values. When the function gets suspended, the state of that function is saved, this includes data like any variable bindings, the instruction pointer, the internal stack, and any exception handling. Paul. We should use yield when we want to iterate over a sequence, but don’t want to store the entire sequence in memory. In effect, a yield-expression is like an inverted function call; the argument to yield is in fact returned (yielded) from the currently executing function, and the return value of yield is the argument passed in via send… Answer: From the “send” method, which can be invoked in place of the “next” function. This means that “yield” must be providing a value to the generator. As in any programming language if we execute a function and it needs to perform some task and have to give its result so … The Python Docs for Yield mention send, and the Python Docs for generator gives the bare-bones description. Python使用yield和send的用法. The “send” method works just like “next”, except that you can pass any Python … ... "yield from" is available since Python 3.3! So, Output: 1 2 3.