Regular Expressions 101

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"
^(?![0]\b)\d+\.
"
gm
^ asserts position at start of a line
Negative Lookahead
(?![0]\b)
Assert that the Regex below does not match
Match a single character present in the list below
[0]
0 matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
\d
matches a digit (equivalent to [0-9])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . with index 4610 (2E16 or 568) 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