Python協程一點理解

• 2020 年 1 月 16 日
• 筆記

yield

def test():      for i in 'abc':          yield i      for i in [1, 2, 3]:          yield i      if __name__ == '__main__':      gen = test()      print(gen.send(None))      print(gen.send(None))      print(gen.send(None))      print(gen.send(None))      print(gen.send(None))      print(gen.send(None))      print(gen.send(None))

def test():      for i in 'abc':          yield i      for i in [1, 2, 3]:          yield i      if __name__ == '__main__':      gen = test()      for i in gen:          print(i)

使用for循環生成器，因為for循環可以捕捉StopIteration異常。

yield from

上面的代碼也可以用yield from實現

def test():      yield from 'abc'      yield from [1, 2, 3]      if __name__ == '__main__':      gen = test()      for i in test():          print(i)

yield from 後面需要加的是可迭代對象，它可以是普通的可迭代對象，也可以是迭代器，甚至是生成器。

使用yield from實現實時計算器

def average_gen():      """      子生成器      """      average = 0      total = 0      count = 0      while True:          num = yield average          if num is None:              break          count += 1          total += num          average = total / count      return average, count, total      def proxy_gen():      """      委派生成器      """      while True:          average, count, total = yield from average_gen()          print(f'平均值{average}, 計算{count}次, 總和{total}')      def client():      """      調用端      """      calc_average = proxy_gen()      calc_average.send(None)      # next(calc_average)      # 預激活協程      print(calc_average.send(10))      print(calc_average.send(20))      print(calc_average.send(30))      calc_average.send(None)      # 關閉協程      if __name__ == '__main__':      client()

在委派生成器中的while True可以替換成for循環，循環的大小決定調用端可以calc_average.send(None)的次數(第一次預激活也計入)。

while True和for循環用來捕捉StopIteration異常，可以查看第一段代碼。

示例

def average_gen():      """      子生成器      """      average = 0      total = 0      count = 0      while True:          num = yield average          if num is None:              break          count += 1          total += num          average = total / count      return average, count, total      def proxy_gen():      """      委派生成器      """      for i in range(2):          average, count, total = yield from average_gen()          print(f'平均值{average}, 計算{count}次, 總和{total}')      def client():      """      調用端      """      calc_average = proxy_gen()      calc_average.send(None)      # next(calc_average)      # 預激活協程      print(calc_average.send(10))      print(calc_average.send(20))      print(calc_average.send(30))      calc_average.send(None)      # 關閉協程      print(calc_average.send(10))      print(calc_average.send(20))      print(calc_average.send(30))      calc_average.send(None)      if __name__ == '__main__':      client()

示例最後會拋出StopIteration異常。

因為在第二次calc_average.send(None)時，for循環捕捉了一次異常，進入了最後一次循環，在calc_average.send(None)時，for不能再次循環，不能處理StopIteration異常，故拋出。