CODEWITHSUNDEEP
pythonregexstring
Yuu10
Yuu10

Reputation: 53

Adding a space after a special character

Im trying to add a space after a special character if there isn't one already in a string.

This is my code

import re
line='Hello there! This is Robert. Happy New Year!Are you surprised?Im not.'
for i in re.finditer(r"\?|!|\.", line):
if line[i.end()]!=' ':
    line=line.replace(line[i.end()],line[i.end()]+' ')

Expected output:

"Hello there! This is Robert. Happy New Year! Are you surprised? Im not."

Output from my code:

"Hello t here!  This is Robert . Happy New Year!A re you surprised? Im not ."

I still haven't figured out why it doesn't work.

Upvotes: 1

Views: 610

Answers (3)

The fourth bird
The fourth bird

Reputation: 163362

In your pattern you use an alternation for 3 characters \?|!|\. that could also be in a single character class [?!.]

What you can do is match either one of them, and assert a non whitespace char other than any of those characters after it, in case you have for example Hi!!

In the replacement you can use the full match using \g<0> followed by a space.

[?!.](?=[^?!.\s])

The pattern matches

  • [?!.] Match either ! . ?
  • (?= Positive lookahead, assert what is directly to the right is
    • [^?!.\s] Match a non whitespace char other than ! . ?
  • ) Close lookahead

See a regex demo and a Python demo.

Example

import re

regex = r"[?!.](?=[^?!.\s])"
line = 'Hi!!Hello there! This is Robert. Happy New Year!Are you surprised?Im not.'
result = re.sub(regex, r'\g<0> ', line)

if result:
    print(result)

Output

Hi!! Hello there! This is Robert. Happy New Year! Are you surprised? Im not.

Upvotes: 1

Cary Swoveland
Cary Swoveland

Reputation: 110685

You can use the following regular expression with re.sub, with (zero-width) matches being replaced by one space:

(?<=[!?.])(?=\S)

(?<=[!?.]) is a negative lookbehind that asserts that the string position is preceded by one of the three characters in the given character class, and the positive lookahead (?=\S) asserts that the current string position is followed by a character other than a whitespace.

Demo

Upvotes: 2

Ryszard Czech
Ryszard Czech

Reputation: 18611

Use

re.sub(r'([!?.])(?=\S)', r'\1 ', line)

See regex proof.

EXPLANATION

--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    [!?.]                    any character of: '!', '?', '.'
--------------------------------------------------------------------------------
  )                        end of \1
--------------------------------------------------------------------------------
  (?=                      look ahead to see if there is:
--------------------------------------------------------------------------------
    \S                       non-whitespace (all but \n, \r, \t, \f,
                             and " ")
--------------------------------------------------------------------------------
  )                        end of look-ahead

Python code:

import re
line='Hello there! This is Robert. Happy New Year!Are you surprised?Im not.'
line = re.sub(r'([!?.])(?=\S)', r'\1 ', line)

Results: Hello there! This is Robert. Happy New Year! Are you surprised? Im not.

Upvotes: 2

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