Support Python 3's 'raise Exception from e'?

[Dan Sully]

It's not clear if tbvaccine supports Python 3's 'raise MyException from e' syntax.

Or at least the original exception is not being emitted in the tbvaccine output.

[Stavros Korokithakis]

Hmm yes, you're right, currently we're printing the last stack frame. This needs to be changed so TBV is more intelligent about which frame it prints.

[Alex Hall]

more intelligent about which frame it prints.

Surely it should print them all?

[Stavros Korokithakis]

It shouldn't expand frames that aren't a part of your program, and doesn't currently.

[Alex Hall]

Let me be clearer. Consider this script:

try:
    1 / 0
except:
    foo

By default it outputs:

Traceback (most recent call last):
  File "/home/alex/.config/JetBrains/PyCharm2020.2/scratches/scratch_856.py", line 6, in <module>
    1 / 0
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/alex/.config/JetBrains/PyCharm2020.2/scratches/scratch_856.py", line 8, in <module>
    foo
NameError: name 'foo' is not defined

This contains two tracebacks. Previously it sounded like you were referring to tracebacks as frames, so I just went with it. Each traceback here contains one frame.

tbvaccine only shows the last traceback:

Traceback (most recent call last):
  File "/home/alex/.config/JetBrains/PyCharm2020.2/scratches/scratch_856.py", line 8, in <module>
>   foo
NameError: name 'foo' is not defined

Presumably tbvaccine should print every traceback so that users know what went wrong, although it can be selective about which frames it prints/expands within each traceback.

Also note that this example doesn't use the raise from syntax.

[Stavros Korokithakis]

Oh, I see. Yes, it definitely shouldn't swallow tracebacks, this is a bug.