[Python-Dev] [Python-checkins] peps: Short subsection on annotating coroutines (Ivan L, #225).

[Brett Cannon]

On Tue, 24 May 2016 at 12:20 guido.van.rossum <python-checkins at python.org>
wrote:

> https://hg.python.org/peps/rev/50c3f5aefbb7
> changeset:   6341:50c3f5aefbb7
> user:        Guido van Rossum <guido at python.org>
> date:        Tue May 24 12:18:54 2016 -0700
> summary:
>   Short subsection on annotating coroutines (Ivan L, #225).
>
> files:
>   pep-0484.txt |  34 ++++++++++++++++++++++++++++++++++
>   1 files changed, 34 insertions(+), 0 deletions(-)
>
>
> diff --git a/pep-0484.txt b/pep-0484.txt
> --- a/pep-0484.txt
> +++ b/pep-0484.txt
> @@ -1015,6 +1015,40 @@
>  ellipsis, i.e. the above example is literally what you would write.
>
>
> +Annotating generator functions and coroutines
> +---------------------------------------------
> +
> +The return type of generator functions can be annotated by
> +the generic type ``Generator[yield_type, send_type,
> +return_type]`` provided by ``typing.py`` module::
> +
> +  def echo_round() -> Generator[int, float, str]:
> +      res = yield
> +      while res:
> +          res = yield round(res)
> +      return 'OK'
> +
> +Coroutines introduced in PEP 492 are annotated with the same syntax as
> +ordinary functions. However, the return type annotation corresponds to the
> +type of ``await`` expression, not to the coroutine type::
> +
> +  async def spam(ignored: int) -> str:
> +      return 'spam'
> +
> +  async def foo():
> +      bar = await spam(42) # type: str
>

If the coroutine has multiple await expressions that return different types
then do you simply use a Union to express that?

-Brett



> +
> +The ``typing.py`` module also provides generic ABCs ``Awaitable``,
> +``AsyncIterable``, and ``AsyncIterator`` for situations where more precise
> +types cannot be specified::
> +
> +  def op() -> typing.Awaitable[str]:
> +      if cond:
> +          return spam(42)
> +      else:
> +          return asyncio.Future(...)
> +
> +
>  Compatibility with other uses of function annotations
>  =====================================================
>
>
> --
> Repository URL: https://hg.python.org/peps
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