Python Regex Pattern Replacement

Question

i'm trying to esssentially get any dynamic input from a python script, in this case its a simple file organizing script. I need to make sure that any instance of [ or ] is wrapped like this [[] []].

So naturally i tried replace but that just put brackets around all of the escape brackets(the escape brackets for using glob.glob)

That proved useless so now i turn to re.sub but i can't seem to find a pattern that will only replace [ or ] with its escape counterpart if the [ or ] has no brackets around it.

I have no idea if that makes sense to anyone but thats pretty much it, here is the messed up re pattern i've got so far, it doesn't like me.

pattern = r'[^\[]([\[])[^\]]'

One problem, how would you if a [ or ] is used for quoting or they should be quoted ? — Ibrahim Najjar
– Ibrahim Najjar, Commented Sep 20, 2013 at 13:51
This is for filenames so basically i just have to escape any square brackets for the purposes of using glob.glob, btw the code worked except i changed [$1] to [\1] after that it was perfect, thanks very much. — Brian Sykes
– Brian Sykes, Commented Sep 20, 2013 at 13:55
Not a solution, but Pyregex can help you in testing patterns out quickly. — Colonel Panic
– Colonel Panic, Commented Sep 20, 2013 at 14:18

Alfe · Accepted Answer · 2013-09-20 14:18:54Z

3

I'd choose a solution using the higher-order feature of re.sub to handle tokens (tokenizing is common practice in parsing computer languages):

def replaceToken(match):
    token = match.group()
    if len(token) == 3:
        return token
    else:
        return '[' + token + ']'

re.sub(r'(\[\[\])|(\[\]\])|\[|\]', replaceToken, 'foo[[bar]bloh')

Or in one call, if you prefer that:

re.sub(r'(\[\[\])|(\[\]\])|\[|\]',
       lambda x: x.group() if len(x.group()) == 3
                           else '[' + x.group() + ']', 'foo[[]bar]bloh')

Results:

'foo[[bar]bloh' → 'foo[[][[]bar[]]bloh'
'foo[[]bar]bloh' → 'foo[[]bar[]]bloh'

answered Sep 20, 2013 at 14:18

Alfe

60.2k21 gold badges117 silver badges172 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Ibrahim Najjar Over a year ago

OK great, the problem is that I don't work with Python so I will ask you for a simple thing and if it worked I will give you my up vote. Could you test this string for me: hello[ from ab ] and this is working []] working so far [[] and what about [[[ or ]][[ ?

Alfe Over a year ago

Returns hello[[] from ab []] and this is working []] working so far [[] and what about [[][[][[] or []][]][[][[] for me. This is what OP wants; I'm skeptic that what he wants makes sense. I guess a better solution would be to find out if the input already is "quoted" using brackets or not and depending on that a quoting should take place, but that's a little out of scope here.

Collectives™ on Stack Overflow

Python Regex Pattern Replacement

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related