Regular Expressions 101

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"
\s(\s)?
"
gm
\s matches any whitespace character (equivalent to [\r\n\t\f\v  ])
1st Capturing Group
(\s)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\s matches any whitespace character (equivalent to [\r\n\t\f\v  ])
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"
gm

Test String

Substitution

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