Forbid to raise exception from itself

[sobolevn]

Rule request

We need to forbid code like raise exc from exc, because it does not make much sense and works the same way:

>>> e = Exception('m')
>>> raise e
Traceback (most recent call last):
  File "ex.py", line 1, in <module>
    e = Exception("m"); raise e
Exception: m

And with from:

>>> e = Exception('m')
>>> raise e from e
Traceback (most recent call last):
  File "ex.py", line 1, in <module>
    e = Exception("m"); raise e
Exception: m

We need to explicitly test two cases:

1. New raise
2. Re-raising inside except

[shruthi223]

Hi! Could you please assign me this? Im new and would like to know more!

[sobolevn]

Hi! @shruthi223 thanks a lot! Take a look at https://github.com/wemake-services/wemake-python-styleguide/blob/master/CONTRIBUTING.md

[shruthi223]

Hi! Been looking into the resources but since I'm a beginner, I haven't been able to make a lot of sense with it. Would it be possible to guide me on how to proceed and maybe what python file I can look at? Thanks!

[sobolevn]

@shruthi223 sure! You need to modify this place: https://github.com/wemake-services/wemake-python-styleguide/blob/master/wemake_python_styleguide/visitors/ast/keywords.py#L54-L63

Write new _check_raise_from_itself method and a new violation inheriting ASTViolation

[singhaditya28]

Hi, I am an aspiring Hacktoberfest an OpenSource newbie. Can I take on this? and is this eligible for hacktoberfest ?

[sobolevn]

@singhaditya28 yes, sure! Thank you!