How to use await expression?

Question

Couldn't figure out how to use await from python 3.5-rc2

>>> async def foo():
...     pass
... 
>>> await foo()
  File "<ipython-input-10-a18cb57f9337>", line 1
    await foo()
            ^
SyntaxError: invalid syntax

>>> c = foo()
>>> await c
  File "<ipython-input-12-cfb6bb0723be>", line 1
    await c
          ^
SyntaxError: invalid syntax

>>> import sys
>>> sys.version
'3.5.0rc2 (default, Aug 26 2015, 21:54:21) \n[GCC 5.2.0]'
>>> del c
RuntimeWarning: coroutine 'foo' was never awaited
>>>

I checked PEP 0492 and that seems like it should be valid. Could they have changed it or something? — TigerhawkT3
– TigerhawkT3, Commented Aug 27, 2015 at 2:35
Have you read this? docs.python.org/3.6/reference/compound_stmts.html#async-def — jeromej
– jeromej, Commented Aug 27, 2015 at 12:41

Railslide · Accepted Answer · 2015-08-27 13:38:53Z

25

As per documentation, await can only be used inside a coroutine function. So the correct syntax for using it should be

async def foo():
    pass

async def bar():
    await foo()

edited Aug 27, 2015 at 13:38

answered Aug 27, 2015 at 13:32

Railslide

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2 Comments

balki Over a year ago

If I have to use the coroutine, I have to create a function and then await on it to get the value?

Railslide Over a year ago

It doesn't necessarily have to be a function, as long as it is an awaitable object (i.e. native and generator-based coroutine or an object with the magic method __await__) @balki

skypjack · Accepted Answer · 2016-02-27 22:30:01Z

7

Just like in C#, await can only be used in an async method (function).

edited Feb 27, 2016 at 22:30

skypjack

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answered Feb 27, 2016 at 22:14

Melf

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