Add space before bracket if there is any character

Question

How can I add space before open bracket ( if there is any character and don't add space if there is a space?

I tried with this expression:

re.sub("\[^}]*\(", ' $1', line)

But it's not working.

How can I check if there is any character before open bracket and if there is no space, add space?

In Python, use `\1` style backreferences with a raw string literal. And you have no capture groups, so you cannot use `\1` here at all. — Wiktor Stribiżew, Apr 11 '16 at 10:37
@anubhava: It also depends whether a space should be inserted if `(` is at the string start. — Wiktor Stribiżew, Apr 11 '16 at 10:40

score 1 · Answer 1 · answered Apr 11 '16 at 10:41

1

Try sub this:

(\w)\(

With this:

\1 (

Demo

answered Apr 11 '16 at 10:41

Kaspar Lee

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score 1 · Accepted Answer · edited May 23 '17 at 10:30

You may use the following regex:

(\S)\(

And replace with r'\1 ('. The (\S) will capture into Group 1 any character that is not a whitespace. Since it is a consuming subpattern, no ( at the string start will get matched (there must be a character before a ().

The backreferences are defined with a backslash in Python (or with \g<n> syntax to make them unambiguous).

Note that to also match a ( at the beginning of a string (to add a space before the first ( in a string), use r'(?<!\s)\(' regex (with a non-consuming subpattern - a negative lookbehind (?<!\s) that makes sure there is no whitespace character before a ():

re.sub(r"(?<!\s)\(", r' (', "(some text)") # => " (some text)"

See the Python demo:

import re
print(re.sub(r"(\S)\(", r'\1 (', "(some text)"))      # => (some text)
print(re.sub(r"(\S)\(", r'\1 (', "Text(some text)"))  # => Text (some text)
print(re.sub(r"(?<!\s)\(", r' (', "(some text)"))     # =>  (some text)

Please note the use of raw string literals to declare both the regex and the regex replacement (this helps avoid many unexpected issues). See What exactly is a “raw string regex” and how can you use it?

Add space before bracket if there is any character

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