\b requires raw strings or to be escaped. Update docs with that hint?

[mlissner]

BPO	29315
Nosy	@bitdancer, @mlissner

^{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 = None
closed_at = <Date 2017-01-18.21:11:54.303>
created_at = <Date 2017-01-18.20:21:15.511>
labels = ['invalid', 'type-feature', '3.7', 'docs']
title = '\\b requires raw strings or to be escaped. Update docs with that hint?'
updated_at = <Date 2017-01-18.21:11:54.301>
user = 'https://github.com/mlissner'

bugs.python.org fields:

activity = <Date 2017-01-18.21:11:54.301>
actor = 'r.david.murray'
assignee = 'docs@python'
closed = True
closed_date = <Date 2017-01-18.21:11:54.303>
closer = 'r.david.murray'
components = ['Documentation']
creation = <Date 2017-01-18.20:21:15.511>
creator = 'Mike.Lissner'
dependencies = []
files = []
hgrepos = []
issue_num = 29315
keywords = []
message_count = 2.0
messages = ['285751', '285755']
nosy_count = 3.0
nosy_names = ['r.david.murray', 'docs@python', 'Mike.Lissner']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue29315'
versions = ['Python 2.7', 'Python 3.3', 'Python 3.4', 'Python 3.5', 'Python 3.6', 'Python 3.7']

[mlissner]

I just ran into a funny corner case I imagine others are aware of. When you write "\b" in Python, it is a single character: "\x08". So if you try to write a regex like:

words = '\b(.*)\b'

That won't work. But using a raw string will:

words = r'\b(.*)\b'

As will escaping it in this horrible fashion:

words = '\\b(.*)\\b'

I believe this doesn't affect any of the other regex flags, so I wonder if it's worth adding something to the docs to warn about this. I just spent a bunch of time trying to figure out why it seemed like \b wasn't working. A little tip in the docs would have gone a LONG way.

[bitdancer]

One should always use raw strings for regex expressions, and this is already documented in the introduction to the regex module. Further, in 3.5 using \ in front of characters that aren't special produces a warning, which should reduce the frequency of this mistake.

I don't see that there's anything to do here.