New submission from Tadhg McDonald-Jensen:
When creating a asynchronous context manager if the __aexit__ method is not
labeled as async (so it returns None instead of a coroutine) the error has a
generic error message:
TypeError: object NoneType can't be used in 'await' expression
Would it be possible to change this so it indicates that it was the context
that was invalid not an `await` statement? Since the traceback points to the
last statement of the with block it can create very confusing errors if the
last statement was an await.
Example:
import asyncio
class Test():
async def __aenter__(self):
print("aenter used")
value = asyncio.Future()
value.set_result(True)
return value
#FORGOT TO MARK AS async !!
def __aexit__(self, *errors):
print("aexit used")
return None
async def my_test():
async with Test() as x:
print("inside async with, now awaiting on", x)
await x
my_test().send(None)
Give the output:
aenter used
inside async with, now awaiting on <Future finished result=True>
aexit used
Traceback (most recent call last):
File ".../test.py", line 19, in <module>
my_test().send(None)
File ".../test.py", line 16, in my_test
await x
TypeError: object NoneType can't be used in 'await' expression
Which indicates to me that `x` was None when it was await-ed for.
----------
components: asyncio
messages: 290630
nosy: Tadhg McDonald-Jensen, yselivanov
priority: normal
severity: normal
status: open
title: error message when __aexit__ is not async
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue29922>
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