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So, 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… Performing a file-system search, a user would be happier to receive results on-the-fly, rather the wait for a search engine to go through … 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 send() method returns the next value yielded by the generator, or raises StopIteration if the generator exits without yielding another value. Return sends a specified value back to its caller whereas Yield can produce a sequence of values. The yield from < expr > statement can be used inside the body of a generator. 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. Python (programming language) Output: 1 2 3. 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. 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. There’s also an async version, although this one has to be awaited. 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. 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. Using the Python "yield" keyword A good example is a search task, where typically there is no need to wait for all results to be found. 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. 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. The Python Docs for Yield mention send, and the Python Docs for generator gives the bare-bones description. This means that “yield” must be providing a value to the generator. When the Python yield statement is hit, the program suspends the function execution and returns the yielded value to the caller. Paul. 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 = [0] * n index = 0 a = 0 b = 1 while index