Regular Expressions 101

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"
(?<=l(?:lo|ut))
"
gm
Positive Lookbehind
(?<=l(?:lo|ut))
Assert that the Regex below matches
l matches the character l with index 10810 (6C16 or 1548) literally (case sensitive)
Non-capturing group
(?:lo|ut)
1st Alternative
lo
lo
matches the characters lo literally (case sensitive)
2nd Alternative
ut
ut
matches the characters ut literally (case sensitive)
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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