Practice>Python>Regex and Parsing>Regex Substitution

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Regex Substitution

Problem Link : https://www.hackerrank.com/challenges/re-sub-regex-substitution/problem

Difficulty : Medium

 

Tip

• It's not a simple replacing string
• You should aware of lookaround, lookahead and lookbegind
• re.sum(r" && ", ' and ', input())
• This is not going to work, if input is like ' && && '
• the space in the middle of two &&
• it consumed when the first && is matched
• so second && can't be matched
• When your pattern is matched, lookaround is included, but the matched string don't have them
• It is a key of lookaround
• So, you should write like below
• re.sub(r"(?<= )(&&)(?= )", 'and', s)
• re.sub(r"(?<= )(\|\|)(?= )", 'or', s)

Please visit below, for more regarding 'lookaround'.

 

https://www.regular-expressions.info/lookaround.html

Solution

import re N = int(input()) for _ in range(N): s = input() s = re.sub(r"(?<= )(&&)(?= )", 'and', s) s = re.sub(r"(?<= )(\|\|)(?= )", 'or', s) print(s)