Clarify recommendation to inherit from Exception

[mdickinson]

BPO	20624
Nosy	@mdickinson, @merwok

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/mdickinson'
closed_at = <Date 2014-04-14.15:35:34.032>
created_at = <Date 2014-02-14.11:31:29.863>
labels = ['docs']
title = 'Clarify recommendation to inherit from Exception'
updated_at = <Date 2014-04-14.15:35:34.030>
user = 'https://github.com/mdickinson'

bugs.python.org fields:

activity = <Date 2014-04-14.15:35:34.030>
actor = 'mark.dickinson'
assignee = 'mark.dickinson'
closed = True
closed_date = <Date 2014-04-14.15:35:34.032>
closer = 'mark.dickinson'
components = ['Documentation']
creation = <Date 2014-02-14.11:31:29.863>
creator = 'mark.dickinson'
dependencies = []
files = []
hgrepos = []
issue_num = 20624
keywords = []
message_count = 5.0
messages = ['211214', '211230', '216090', '216096', '216097']
nosy_count = 4.0
nosy_names = ['mark.dickinson', 'eric.araujo', 'docs@python', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue20624'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5']

[mdickinson]

From http://docs.python.org/3.4/library/exceptions.html:

"... programmers are encouraged to at least derive new exceptions from the Exception class and not BaseException."

This wording had someone I've talked to recently thinking that user-defined exceptions should inherit *directly* from Exception.

Suggested rewording, dropping the "at least" qualification that as far as I can tell serves no real purpose:

"... programmers are encouraged to derive new exceptions from the Exception class or one of its subclasses, and not from BaseException."

[merwok]

In my reading “at least” means that exceptions should derive from Exception if they don’t derive from a more specific subclass. IOW the same meaning as your proposed wording, but less clear. +1 to your rewording.

[python-dev]

New changeset 8dc1b45bd467 by Mark Dickinson in branch '3.4':
Issue bpo-20624: Exception docs wording tweak - clarify that it's okay to inherit from a subclass of Exception.
http://hg.python.org/cpython/rev/8dc1b45bd467

New changeset 262204877004 by Mark Dickinson in branch 'default':
Issue bpo-20624: Merge exception docs tweak from 3.4 branch.
http://hg.python.org/cpython/rev/262204877004

[python-dev]

New changeset f729a0e90c4f by Mark Dickinson in branch '2.7':
Issue bpo-20624: Merge exception docs tweak from 3.4 branch.
http://hg.python.org/cpython/rev/f729a0e90c4f

[mdickinson]

Fixed. Closing.