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This issue is about how if a coroutine is wrapped in a Task with asyncio.ensure_future(), then portions of the exception chain can be lost.
Specifically, if you run the following code, then ValueError will be raised with exc.__context__ equal to the KeyError:
 import asyncio
 async def raise_error():
 raise ValueError
 async def main():
 try:
 raise KeyError
 except Exception as exc:
 future = raise_error()
 # Uncommenting the next line makes exc.__context__ None below.
 # future = asyncio.ensure_future(future)
 try:
 await future
 except Exception as exc:
 print(f'error: {exc!r}, context: {exc.__context__!r}')
 raise
 asyncio.get_event_loop().run_until_complete(main())
However, if you uncomment the `asyncio.ensure_future()` line, then the ValueError will be raised with no __context__.
I originally raised this issue a couple years ago here:
https://mail.python.org/pipermail/async-sig/2017-November/000403.html
There it was suggested that this was a special case of this issue:
https://bugs.python.org/issue29587
However, after writing code to fix that, this issue still exists.