Regular Expressions 101

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"
^\d\d?(?:\.\d\d?)?(?:\.\d\d?)?$
"
^ asserts position at start of the string
\d matches a digit (equivalent to [0-9])
\d
matches a digit (equivalent to [0-9])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
Non-capturing group
(?:\.\d\d?)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
\d matches a digit (equivalent to [0-9])
\d
matches a digit (equivalent to [0-9])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
Non-capturing group
(?:\.\d\d?)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
\d matches a digit (equivalent to [0-9])
\d
matches a digit (equivalent to [0-9])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"

Test String