Regular Expressions 101

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/
(1\s?)?(\d{3}|\(\d{3}\))[\-\s]?\d{3}[\-\s]?\d{4}
/
gm
1st Capturing Group
(1\s?)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
1 matches the character 1 with index 4910 (3116 or 618) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
2nd Capturing Group
(\d{3}|\(\d{3}\))
1st Alternative
\d{3}
\d
matches a digit (equivalent to [0-9])
{3} matches the previous token exactly 3 times
2nd Alternative
\(\d{3}\)
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
\d
matches a digit (equivalent to [0-9])
{3} matches the previous token exactly 3 times
\) matches the character ) with index 4110 (2916 or 518) literally (case sensitive)
Match a single character present in the list below
[\-\s]
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
\s matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
\d
matches a digit (equivalent to [0-9])
{3} matches the previous token exactly 3 times
Match a single character present in the list below
[\-\s]
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
\s matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
\d
matches a digit (equivalent to [0-9])
{4} matches the previous token exactly 4 times
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

/
/
gm

Test String

Code Generator

Generated Code

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Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report.
For a full regex reference for Python, please visit: https://docs.python.org/3/library/re.html