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Given a string, I need to replace a substring with another in an area not located between two given words.

For example:

substring: "ate" replace to "drank", 1st word - "wolf", 2nd word - "chicken"

input:  The wolf ate the chicken and ate the rooster
output: The wolf ate the chicken and drank the rooster

Currently, the only solution I have is extremely unclean:

1) Replace the string located between the two words to a temporary substring, via Replace a string located between

2) replace the string I originally wanted

3) revert the temporary string to the original string

Edit:

I specifically asked a slightly different question than my case to keep the answer relevant for future readers.

My specific need is splitting a string according to ":", when I need to disregard ":" that are between "<" and ">" brackets that can be chained, where the only promise is that the number of opening brackets equal the number of closing brackets.

So for example, In the following case:

input  a : <<a : b> c> : <a < a < b : b> : b> : b> : a
output [a, <<a : b> c>, <a < a < b : b> : b> : b>, a]

If the answers are very different, I'll start another question.

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8
  • wolf: {, chicken: }, ate:a. Are any of these possible: "a { a a } a", "a {a} a {a} a", "{a {a} }", "{a} a a"? Can you edit the question to explain some more cases? Commented Apr 16, 2015 at 12:58
  • yes, especially {a {a} }, in which case none of these "a" should be changed. Commented Apr 16, 2015 at 13:01
  • In Python, are you using re or regex? Have you considered a non-regex solution? Commented Apr 16, 2015 at 13:05
  • re, python 2.7, but same applies for 3.4 Commented Apr 16, 2015 at 13:09
  • With all the cases in my comment (and more), I'd take a risk and say you cannot do it with a Python re regex. With the regex module you have recursion (IIRC), but I'm not sure you want to go there either. Write a loop, count { and }, and replace when count is 0. Commented Apr 16, 2015 at 13:19

2 Answers 2

Reset to default
3 
def repl(match):
    if match.group()=="ate":
        return "drank"
    return  match.group()


x="The wolf ate the chicken and ate the rooster"
print re.sub(r"(wolf.*chicken)|\bate\b",repl,x)

You can use a function for replacement to do the trick with re.sub

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1 Comment

This is what I meant :)
1

Use re.sub one-liner function.

>>> s = "The wolf ate the chicken and ate the rooster"
>>> re.sub(r'wolf.*?chicken|\bate\b', lambda m: "drank" if m.group()=="ate" else m.group(), s)
'The wolf ate the chicken and drank the rooster'

Update:

Updated problem would be solved by using regex module.

>>> s = "a : <<a : b> c> : <a < a < b : b> : b> : b> : a"
>>> [i for i in regex.split(r'(<(?:(?R)|[^<>])*>)|\s*:\s*', s) if i]
['a', '<<a : b> c>', '<a < a < b : b> : b> : b>', 'a']

DEMO

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5 Comments

The DEMO link isn't working properly, the attached python example works perfectly.
yep, it shows only the captured text. Added just to show how nested <> are captured.
I did find a problem: a< b <c a>> (no ":" )is being split into ['a', '< b <c a>>']. I don't want to pre-optimize, but I have no idea what's the performance relative to a tailored non-regex solution.
if you have any further problems, please ask it as a new question along with the sample input and expected output.
asked a follow up question - stackoverflow.com/questions/29727339/…

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