"W602 deprecated form of raising exception" with "raise t, v, tb" about pycodestyle

[paulegan]

I came across the same issue recently.

I think the preferred form for your example would be:

try:
    foo()
except Exception, error:
    try:
        bar()
    except:
        pass
    raise error

However if you want to raise a different exception, while preserving the original traceback, then I think you gave to break PEP8 and use the "old" form:

raise MyError, sys.exc_value, sys.exc_traceback

[jerdfelt]

Unfortunately the proposed "preferred form" changes the behavior. While it raises the original exception, it changes the traceback, which pretty much makes the traceback useless.

The three-arg form of raise looks to be the only way to raise the original exception and preserve the traceback.

[rconradharris]

I've been searching around and can't find any confirmation that the 3-arg raise is deprecated for Python 2.x. Anybody able to turn up an official statement regarding this?

(Python 3 can preserve the traceback using the with_exception method; given that this is not an option in Python 2.x, might not make sense to deprecate the only way of re-raising an exception with the original traceback.)

[fdr]

I also have code that attempts to preserve the original traceback and thusly annoys pep8, which I feel it shouldn't since nobody has produced any other option that has the same semantics.

[clayg]

use:
raise t(*v.args), None, tb

until fix is merged:
#50

[florentx]

Should be fixed in 0.7.
Thank you for the patch.

[ajdavis]

I think we have to reopen this. pep8 version 1.4.6 on this file:

import sys


def f():
    try:
        raise Exception('foo')
    except:
        e, v, t = sys.exc_info()
        raise Exception, Exception("f"), t

causes:

foo.py:9:24: W602 deprecated form of raising exception

[xsleonard]

This is getting W602, should it not be?

pep 1.5.7

import sys


def f():
    try:
        raise ValueError
    except ValueError as e:
        raise e, None, sys.exc_info()[2]

[florentx]

well, the check for W602 is regex-based, and it's not obvious to avoid such false positive.

btw, you could probably rewrite the expression with a more readable syntax

import sys


def f():
    try:
        raise ValueError
    except ValueError:
        (exc, exc_type, tb) = sys.exc_info()
        raise exc, None, tb

[mforbes]

@florentx You might like to check the order of your arguments in your suggestion: I think it best be (exc_type, exc, tb) = sys.exc_info().