CODEWITHSUNDEEP
pythonregex
harshal1618
harshal1618

Reputation: 61

How to switch two elements in string using Python RegEx?

I am trying to switch two elements in the string while keeping all the other characters untouched. Here is an example:

Original string: 

r'xyzA*12*pqR*stB*HS*lmN*opA*45*a4N*gB*SD*drtU*ghy'

Required output: 

r'xyzA*HS*pqR*stB*12*lmN*opA*SD*a4N*gB*45*drtU*ghy'

Notice that element after A* and B* are switched.

I was able to compile a RegEx pattern that gives me elements to replace like following:

>>> import re
>>> pattern = re.compile(r'A\*(.*?)\*.*?B\*(.*?)\*')
>>> M = pattern.findall(string)
>>> M
[('12', 'HS'), ('45', 'SD')]

After this stage I need your help to find out how to use sub to get the required string.

Upvotes: 5

Views: 601

Answers (2)

fyrescyon
fyrescyon

Reputation: 21

Alternatively, you could also solve this with string find and a loop instead of regular expressions:

str = r'xyzA*12*pqR*stB*HS*lmN*opA*45*a4N*gB*SD*drtU*ghy'
result = ""
start = 0
while (str.find("A*", start) > -1):
        aStart = str.find("A*", start)+2
        aEnd = str.find("*", aStart)
        bStart = str.find("B*", aEnd)+2
        bEnd = str.find("*", bStart)
        result += str[start:aStart]+str[bStart:bEnd]+str[aEnd:bStart]+str[aStart:aEnd]
        start = bEnd
result += str[start:]

print result
#xyzA*HS*pqR*stB*12*lmN*opA*SD*a4N*gB*45*drtU*ghy

Upvotes: 1

akuiper
akuiper

Reputation: 214927

One option is to capture the pattern between the two interested patterns as well and use back reference to reorder them:

s = r'xyzA*12*pqR*stB*HS*lmN*opA*45*a4N*gB*SD*drtU*ghy'

import re
pattern = re.compile(r'A\*(.*?)(\*.*?B\*)(.*?)\*')

#keep the position of the second group and switch the position of the first and third group
pattern.sub(r"A*\3\2\1*", s)
# 'xyzA*HS*pqR*stB*12*lmN*opA*SD*a4N*gB*45*drtU*ghy'

Upvotes: 8

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