1. yield 中 send 用法
- send 作用 – 生成器函数返回值给调用方； – 调用方通过 send 传入值给生成器函数；
- 示例：
>>> def name_func():
... yield_result = 0
... while 1:
... yield_result += 1
... send_value = yield yield_result # 这一句是关键！！！
... print(f"func has been sent value : {send_value}")
...
>>>
>>> gen = name_func()
>>> # print(next(gen))
... print("yield_result : ", gen.send(None)) # 第一次调用, send 传入 None
yield_result : 1
>>> print("yield_result : ", gen.send("lavra"))
func has been sent value : lavra
yield_result : 2
>>> print("yield_result : ", gen.send("hiton"))
func has been sent value : hiton
yield_result : 3
上面的代码示例中，最关键的一句是：send_value = yield yield_result，其中： – send_value 是被 send 传入函数的值； – yield_result 是返回给调用方 gen 的值；
- next 和 send 的区别: – next 只能取值； – send 能取本次yield的返回值，也能给上次yield传入值；
-
send 注意点： – 第一个 send 不能给 yield 传值，必须要 send None，这一步不能省！
- 应用示例
>>> def url_repository(): ... url_list = [] ... while True: ... # _url 是 send 发送给 yield 的参数值，在接下来的语句中使用， ... _url = yield url_list # url_list是 yield 的返回值 ... url_list.append(_url) ... print(f"ADD URL : {_url}") ... >>> >>> g = url_repository() # 实例化生成器函数 >>> g.send(None) # 第一次调用, send 传入 None [] >>> print("URL REPO : ", g.send('url_1')) # g.send() 返回 url_list ADD URL : url_1 URL REPO : ['url_1'] # 打印 yield 返回的 url_list >>> print("URL REPO : ", g.send('url_2')) ADD URL : url_2 URL REPO : ['url_1', 'url_2'] >>> print("URL REPO : ", g.send('url_3')) ADD URL : url_3 URL REPO : ['url_1', 'url_2', 'url_3']2. yiled from 用法
- 下面是一个 yiled 生成器：
>>> def func(): ... for num in range(0, 5): ... yield num ... >>> >>> g = func() >>> print(next(g)) 0 >>> print(next(g)) 1 >>> print(next(g)) 2 >>> print(next(g)) 3 >>> print(next(g)) 4 >>> print(next(g)) Traceback (most recent call last): File "<stdin>", line 1, in <module> StopIteration - 我们可以将其改成如下代码：
>>> def func(): ... yield from range(5) ... >>> >>> g = func() >>> print(next(g)) 0 >>> print(next(g)) 1 >>> print(next(g)) 2 >>> print(next(g)) 3 >>> print(next(g)) 4 >>> print(next(g)) Traceback (most recent call last): File "<stdin>", line 1, in <module> StopIteration
