re.sub not working

[snippsat]

Hello, Do you know how can we format string to raw string? I've googled it but that not work

You add r(raw string) to the regex pattern,do this always as a habit or can get problems.
Example add car after new line(\n).

>>> import re
>>> 
>>> s = ' hello world\n'
>>> re.sub('(\n)', '\1car', s)
' hello world\x01car

So it fails,now add r and it's ok.

>>> import re
>>> 
>>> s = ' hello world\n'
>>> re.sub(r'(\n)', r'\1car', s)
' hello world\ncar'

From regex doc.

The solution is to use Python’s raw string notation for regular expression patterns;
backslashes are not handled in any special way in a string literal prefixed with 'r'.
So r"\n" is a two-character string containing '\' and 'n', while "\n" is a one-character string containing a newline.
Usually patterns will be expressed in Python code using this raw string notation.