python regex not matching when regex tools indicate it should

Question

I have an if statement in a script to see if a directory given via argparse is a UNC path. But does not end with a trailing slash.

import re

#dest is set by argparse. but for this purpose i'll set it manually.
#originally i was escaping each \ in dest. But I found that argparse left them alone.
dest = '\\server-name\folder\subfolder'

if re.match ('^\\+[\w\W]+', dest ) and not re.match( '^\\+[\w\W]+\\$', dest):
    dest = dest + '\\'

I've been playing with this in ipython. The first statement is failing to match. I used the RxToolkit in Komodo IDE, it shows the regex as matching. I tried this webtool: http://www.pythonregex.com/ it matches as well. Any ideas?

Jerry · Accepted Answer · 2014-03-17 13:50:40Z

5

You are passing this to the re:

^\+[\w\W]+

Because \\ means \. What you need to do is to raw your regex strings, by using r:

if re.match(r'^\\+[\w\W]+', dest ) and not re.match(r'^\\+[\w\W]+\\$', dest):
            ^                                       ^

answered Mar 17, 2014 at 13:50

Jerry

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falsetru · Accepted Answer · 2014-03-17 13:49:32Z

4

The string "\\" represent a single backslash \.

>>> print('\\')
\

You need to escape \ or should use raw string literal to represent two backslashes.

>>> print('\\\\')
\\
>>> print(r'\\')
\\

BTW, re.match check for match at the beginning of the string; you can omit the leading ^.

answered Mar 17, 2014 at 13:49

falsetru

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