Title: raise an exception from multiple positions break the traceback frames
Type: behavior Stage:
Components: Versions: Python 3.6
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: hubo1016
Priority: normal Keywords:

Created on 2018-03-13 09:19 by hubo1016, last changed 2018-03-13 09:19 by hubo1016.

File name Uploaded Description Edit hubo1016, 2018-03-13 09:19 demonstration script
Messages (1)
msg313735 - (view) Author: hubo (hubo1016) * Date: 2018-03-13 09:19
The attachment is a script that demonstrates the behavior. The simple unittest script should exit very quickly, but in fact, it runs indefinitely.

It uses asyncio to reproduce the result, but other concurrent technologies are also affected.

In Python 3, traceback of an exception is mutable. When the exception is re-raised, current frames are appended to the traceback. But when the same exception object is raised in multiple position (e.g. passed to different coroutines with futures), the frames are appended in the same list, so the tracebacks are mixed together.

assertRaises in unittest calls traceback.clear_frames internally. When the tracebacks are mixed, it may clear a running frame (in a generator), producing strange behaviors.
Date User Action Args
2018-03-13 09:19:42hubo1016create