[issue35867] NameError is not caught at Task execution

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

I do not think this is a bug. Any exception that is raised inside a task will 
be in the .exception() method when the task is finished. Here you are running 
the task without waiting for finalization. For example, if you change:

async def cofunc1(self):
await self.cofunc2()
await self.task # <-
print("\nwaitin' : where-t-f is the NameError hiding!?")
await asyncio.sleep(6)
print("Wait is over, let's exit\n")

you will find the NameError immediately. If you do not want to await the task 
you can wait until self.task.done() is True and then check 
self.task.exception() for retrieving the exception (if any).

What happens with BaseException is that is a very low-level exception that is 
handled differently compared with regular exceptions that derive from 
Exception. The reason is that control flow exceptions and things like 
KeyboardInterrupt need to be handled differently. This happens explicitly here:

https://github.com/python/cpython/blob/master/Modules/_asynciomodule.c#L2675

--
nosy: +pablogsal
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue35867] NameError is not caught at Task execution

[Emmanuel Arias]

Emmanuel Arias  added the comment:

I test it and this have the same behavior on 3.7 and 3.8...

I will work on this

--
nosy: +eamanu
versions: +Python 3.7, Python 3.8

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[issue35867] NameError is not caught at Task execution

[Sampsa Riikonen]

New submission from Sampsa Riikonen :

- Create a cofunction that raises an Exception or an Error
- Schedule that cofunction as a task
- Exceptions are raised when the task is executed OK
- However, Errors (i.e. NameError, AssertionError, etc.) are raised only at 
task garbage collection..!

Please try this snippet:

```
import asyncio

class HevonPaskaa:

def __init__(self):
pass

async def goodfunc(self):
await asyncio.sleep(3)
print("Good function was called allright")
print("While it was sleeping, hevonpaska must have been executed")

async def hevonpaska(self):
"""When this cofunction is scheduled as a task:
- The NameError is not raised immediately .. !
- BaseException is raised immeadiately OK
"""
raise NameError # WARNING: This is catched only when the program 
terminates
# raise BaseException # WARNING: comment the previous line and 
uncomment this: this is catched immediately

async def cofunc2(self):
# # we'd like this to raise the NameError immediately:
self.task = asyncio.get_event_loop().create_task(self.hevonpaska())
self.good_task = asyncio.get_event_loop().create_task(self.goodfunc())
# # this raises NameError immediately because the task is garbage 
collected:
# self.task = None

async def cofunc1(self):
await self.cofunc2()
print("\nwaitin' : where-t-f is the NameError hiding!?")
await asyncio.sleep(6)
print("Wait is over, let's exit\n")

hv = HevonPaskaa()

asyncio.get_event_loop().run_until_complete(hv.cofunc1())
```

--
components: asyncio
messages: 334625
nosy: Sampsa Riikonen, asvetlov, yselivanov
priority: normal
severity: normal
status: open
title: NameError is not caught at Task execution
type: behavior
versions: Python 3.6

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