raise-missing-from.md

Pattern: Missing use of raise from

Issue: -

Description

Python 3's exception chaining means it shows the traceback of the current exception, but also the original exception. Not using raise from makes the traceback inaccurate, because the message implies there is a bug in the exception-handling code itself, which is a separate situation than wrapping an exception.

Example of incorrect code:

try:
    1 / 0
except ZeroDivisionError:
    # +1: [raise-missing-from]
    raise KeyError

Example of correct code:

try:
    1 / 0
except ZeroDivisionError:
    raise KeyError from foo