Now typecheckes traceback in raise e, msg, traceback on py2

[sobolevn]

No description provided.

[sobolevn]

I found several other corner-cases, which I want to cover later today.

[sobolevn]

Corner cases:

1. Old styled classes are allowed to be used with raise in python2:

class Old:
    pass

raise Old

# Traceback (most recent call last):
#  File "Main.py", line 4, in <module>
#    raise Old
# __main__.Old: <__main__.Old instance at 0x14ada04a35f0>

I don't think that we should ever support this. First of all, mypy does not have any old-styled / new-styled distinction.
Secondly, it will require a lot of work to add this.

2. raise can be used with tuple like this:

e = (Exception, 2, 3, 4, 5, 6, 7, 8)  # or `Exception('a')`
raise e

# Traceback (most recent call last):
#  File "Main.py", line 8, in <module>
#    raise e
# Exception

This is something we can clearly support. I will add this to this PR.

3. This, on the other side is not allowed:

e = Exception('a')  # Or `(Exception('a'),)`
raise e, 'b'
# TypeError: instance exception may not have a separate value

I will add a check for that as well.

4. Case with callable exception type:

class My(Exception):
    def __init__(self, start, finish):
        pass

raise My, 1  # should raise

Currently, we don't support this. But in runtime if fails:

Traceback (most recent call last):
  File "Main.py", line 8, in <module>
    raise My, 1
TypeError: __init__() takes exactly 3 arguments (2 given)

We need to check this similarly to Python3.

[JelleZijlstra]

This seems fine, but honestly it doesn't feel that valuable to fix arcane aspects of Python 2 raise syntax. Python 2 support is a low priority already and we may drop support at some point.

If this solves problems in your codebase, though, I'm happy to review and merge it.

[sobolevn]

If this solves problems in your codebase, though, I'm happy to review and merge it.

Not production code, fortunately 🙂
I was teaching how to use python2 (for historic reasons) and type annotations there. And got hit by this.

and we may drop support at some point

Sure thing! Right now it would be even easier: because all python2 related code for this feature now lives in a separate protected function with _python2 postfix. We can just remove it later and done! 👏

@JelleZijlstra it's now ready to be reviewed.

[JelleZijlstra]

Thanks! I have two small comments.

[JelleZijlstra]

Why not make it a constructor argument?

[sobolevn]

Because we only use it in fastparse2 and nowhere else. It would be easier to remove one day.

[sobolevn]

Thanks! 🎉