如何使用等待表达？

Question

无法从Python3.5-rc2中找出如何使用await

>>> 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
>>> 

Answer 1

根据documentation，await只能在协程函数内部使用。所以正确的语法应该是

async def foo():
    pass

async def bar():
    await foo()

Answer 2

就像在C中一样，await只能在async方法（函数）中使用。