New submission from Ben Hoyt: In the official tutorial in the "User-defined Exceptions" section (https://docs.python.org/3.5/tutorial/errors.html#user-defined-exceptions) there's a note about a user-defined Exception subclass as follows:
"In this example, the default __init__() of Exception has been overridden. The new behavior simply creates the value attribute. This replaces the default behavior of creating the args attribute." That last sentence is wrong: it used to be that way (it is in Python 2.x and I believe in Python pre 3.2), but now the implementation of BaseException.__new__ now sets args, so even when you override __init__ and don't call super() args is set. I think that's what you want, so I'm putting this down to a documentation bug. I think the sentence "This replaces the default behavior of creating the args attribute." should simply be removed (BaseException.__init__ basically does nothing now). This change happened for Python 3.3 and was backported to Python 3.2. See also: * The relevant part of BaseException.__new__ in the CPython codebase: https://github.com/python/cpython/blob/601ee5fab5df81a25611da0667030de531c1cda9/Objects/exceptions.c#L44-L48 * The issue where this behaviour was changed: http://bugs.python.org/issue1692335 * The commit where it was changed: https://hg.python.org/cpython/rev/68e2690a471d (on GitHub at https://github.com/python/cpython/commit/a71a87e695b05a67bd22c6ac74311b1f56f3932e) * You can repro this and confirm that "args" is definitely set with the attached script: $ python exception_args_test.py sys.version_info(major=3, minor=5, micro=2, releaselevel='final', serial=0) Error args: ('error!',) ---------- assignee: docs@python components: Documentation files: exception_args_test.py messages: 272256 nosy: benhoyt, docs@python, georg.brandl, sbt priority: normal severity: normal status: open title: Misleading note about "args" attribute in "User-defined Exceptions" section of tutorial versions: Python 3.2, Python 3.3, Python 3.4, Python 3.5, Python 3.6 Added file: http://bugs.python.org/file44058/exception_args_test.py _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue27719> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
