yield from关键字是在：PEP 380 -- Syntax for Delegating to a Subgenerator 中提出的
用于生成器将其部分操作委托给另外一个生成器，这允许将包含yield的一段代码分解出来并放在另外一个生成器中，此外，允许子生成器返回一个值，这个值可供委派生成器使用
from collections import namedtuple Result = namedtuple("Result", "count average") li = [40.9, 38.5, 44.3] # 子生成器 def averager(): total = 0.0 count = 0 average = None while True: term = yield print("====", term) if term is None: break total += term count += 1 average = total / count return Result(count, average) # 委派生成器 def grouper(result, key): while True: result[key] = yield from averager() # 调用方 def main(): results = {} group = grouper(results, "kg") next(group) # 调入 委派生成器, 然后调入子生成器，到yield for value in li: group.send(value) # 直接传递到子生成器的yield group.send(None) # group.send(None) # print(results) if __name__ == "__main__": main()
yield from的主要功能是打开双向通道，把最外层的调用方与最内层的子生成器连接起来，这样二者可以直接发送和产出值，还可以直接传入异常
关于yield from 六点重要的说明：
import sys import time def binary(n): if n <= 0: return 1 l = yield from binary(n - 1) r = yield from binary(n - 1) return l + 1 + r async def abinary(n): if n <= 0: return 1 l = await abinary(n - 1) r = await abinary(n - 1) return l + 1 + r def timeit(func, depth, repeat): t0 = time.time() for _ in range(repeat): o = func(depth) print(o) try: while True: o.send(None) except StopIteration: pass t1 = time.time() print(‘{}({}) * {}: total {:.3f}s‘.format( func.__name__, depth, repeat, t1 - t0)) # timeit(binary, 19, 30) # binary(19) * 30: total 7.388s # timeit(abinary, 19, 30) # abinary(19) * 30: total 7.357s # 2着用时基本一致
原文：https://www.cnblogs.com/glh-ty/p/11081986.html