Python3基础 yield send 获得生成器后，需要先启动一次

 

•        Python : 3.7.3
•          OS : Ubuntu 18.04.2 LTS
•         IDE : pycharm-community-2019.1.3
•       Conda : 4.7.5
•    typesetting : Markdown

 

code

"""
@Author : 行初心
@Date   : 2019/7/6
@Blog   : www.cnblogs.com/xingchuxin
@Gitee  : gitee.com/zhichengjiu
"""


def yield_test():
    # next() 遇到yield会停止，保存数据并返回后面的数值
    # send_value默认为None
    a = 1
    send_value = yield a + 1
    print(send_value)

    send_value = yield a + 1
    print(send_value)


def main():
    # 获得生成器
    generator = yield_test()

    # 启动 - 第一种方式
    print(id(generator), generator.__next__())

    # 想理解好 send 的功能，建议使用 Debug - Step Into(F7)。一步一步地跟下来
    print(generator.send("hello"))

    print("---")

    # 获得生成器
    generator = yield_test()

    # 启动 - 第二种方式
    print(id(generator), generator.send(None))
    print(generator.send("world"))

    print("---")


if __name__ == '__main__':
    main()

 

result

/home/coder/anaconda3/envs/py37/bin/python /home/coder/PycharmProjects/NumericalComputation/demo.py
140581898176336 2
hello
2
---
140581898176456 2
world
2
---

Process finished with exit code 0

 

source_code

class Generator(Iterator[_T_co], Generic[_T_co, _T_contra, _V_co]):
    @abstractmethod
    def __next__(self) -> _T_co: ...

    @abstractmethod
    def send(self, value: _T_contra) -> _T_co: ...

    @abstractmethod
    def throw(self, typ: Type[BaseException], val: Optional[BaseException] = ...,
              tb: Optional[TracebackType] = ...) -> _T_co: ...

    @abstractmethod
    def close(self) -> None: ...

    @abstractmethod
    def __iter__(self) -> Generator[_T_co, _T_contra, _V_co]: ...

    @property
    def gi_code(self) -> CodeType: ...
    @property
    def gi_frame(self) -> FrameType: ...
    @property
    def gi_running(self) -> bool: ...
    @property
    def gi_yieldfrom(self) -> Optional[Generator]: ...

# TODO: Several types should only be defined if sys.python_version >= (3, 5):
# Awaitable, AsyncIterator, AsyncIterable, Coroutine, Collection.
# See https: //github.com/python/typeshed/issues/655 for why this is not easy.

 

more_knowledge

code

"""
@Author : 行初心
@Date   : 2019/7/6
@Blog   : www.cnblogs.com/xingchuxin
@Gitee  : gitee.com/zhichengjiu
"""


def yield_test():
    a = 1
    send_value = yield a + 1
    print(send_value)


def main():
    # 获得生成器
    generator = yield_test()
    # 直接用send("hello world")
    generator.send("hello world")


if __name__ == '__main__':
    main()

result

/home/coder/anaconda3/envs/py37/bin/python /home/coder/PycharmProjects/NumericalComputation/demo.py
Traceback (most recent call last):
  File "/home/coder/PycharmProjects/NumericalComputation/demo.py", line 29, in <module>
    main()
  File "/home/coder/PycharmProjects/NumericalComputation/demo.py", line 25, in main
    generator.send("hello world")
TypeError: can't send non-None value to a just-started generator

Process finished with exit code 1

 

reference

• https://www.cnblogs.com/xhcdream/p/8304953.html

 

resource

• [文档 - English] docs.python.org/3
• [文档 - 中文] docs.python.org/zh-cn/3
• [规范] www.python.org/dev/peps/pep-0008
• [规范] zh-google-styleguide.readthedocs.io/en/latest/google-python-styleguide/python_language_rules
• [源码] www.python.org/downloads/source
• [ PEP ] www.python.org/dev/peps
• [平台] www.cnblogs.com
• [平台] gitee.com

 

---

Python具有开源、跨平台、解释型、交互式等特性，值得学习。
Python的设计哲学：优雅，明确，简单。提倡用一种方法，最好是只有一种方法来做一件事。
代码的书写要遵守规范，这样有助于沟通和理解。
每种语言都有独特的思想，初学者需要转变思维、踏实践行、坚持积累。