CODEWITHSUNDEEP
pythonregex
Arcadia_Lake
Arcadia_Lake

Reputation: 119

Python - Using regex to write a function imitating the strip() method

I am doing a problem from Automate the Boring Stuff, trying to imitate the strip() method using regex. I have pretty much figured it out, works with whitespace and a specific word I want removed. But when removing a specific keyword from the end of a string, it always cuts the last letter of the string off, can anyone help me figure out why?

def strip_func(string, *args):
strip_regex = re.compile(r'^(\s+)(.*?)(\s+)$')
mo = strip_regex.findall(string)
if not mo:
    rem = args[0]
    remove_regex = re.compile(rf'({rem})+(.*)[^{rem}]')
    remove_mo = remove_regex.findall(string)
    print(remove_mo[0][1])

else:
    print(mo[0][1])

So if no second argument is passed then the function deletes whitespace from either side of the string, I used this string to test that:

s = '        This is a string with whitespace on either side        '

Otherwise it deletes the keyword, kind of like the strip function. Eg:

spam = 'SpamSpamBaconSpamEggsSpamSpam'
strip_func(spam, 'Spam')

Output:

BaconSpamEgg

So missing the 's' at the end of Eggs, same thing happens with every string I try. Thanks in advance for the help.

Upvotes: 2

Views: 134

Answers (1)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 626950

You may use

import re

def strip_func(string, *args):
  return re.sub(rf'^(?:{re.escape(args[0])})+(.*?)(?:{re.escape(args[0])})+$', r'\1', string, flags=re.S)

spam = 'SpamSpamBaconSpamEggsSpamSpam'
print(strip_func(spam, 'Spam'))

See the Python demo. The ^(?:{re.escape(args[0])})+(.*?)(?:{re.escape(args[0])})+$ pattern will create a pattern like ^(?:Spam)+(.*?)(?:Spam)+$ and will match

  • ^ - start of string
  • (?:Spam)+ - one or more occurrences of Spam at the start of the string
  • (.*?) - Group 1: any 0 or more chars as few as possible
  • (?:Spam)+ - one or more occurrences of Spam at the start of the string
  • $ - end of string.

The flags=re.S will make . match line break chars, too.

Upvotes: 2

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