Regular Expressions 101

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Function

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  • Unit Tests (37)
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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Character class intersection
    [\w&&[^\d]]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
Processing...

Test String

Code Generator

Language

Generated Code

import re regex = re.compile(r"(?<=\D|^)(?<year>\d{4})(?<sep>[^\w\s])(?<month>1[0-2]|0[1-9])\k<sep>(?<day>0[1-9]|[12][0-9]|(?<=11\k<sep>|[^1][4-9]\k<sep>)30|(?<=1[02]\k<sep>|[^1][13578]\k<sep>)3[01])(?=\D|$)", flags=re.MULTILINE) test_str = ("\n" "2020-01-01\n" "2020-01-31\n" "2020-02-29\n" "2020-03-31\n" "2020-04-30\n" "2020-05-31\n" "2020-06-30\n" "2020-07-31\n" "2020-08-31\n" "2020-09-30\n" "2020-10-31\n" "2020-11-30\n" "2020-12-31\n" "2020-01-01 00:00:00,000\n" "2020-01-01_00:00:00,000\n" "2020-01-01-00:00:00,000\n" "2020-01-01T00:00:00,000\n" "2222-01-01\n" "2222/11/22\n" "2222.11.22\n\n" "// Invalid dates\n" "2020-00-01\n" "2020-01-00\n" "000-01-01\n" "222-01-01\n" "2020-1-1\n" "2020-1-01\n" "2020-01-1\n" "2020-22-01\n" "2020-01-33\n" "2020-01-32\n" "2020-02-30\n" "2020-03-32\n" "2020-04-31\n" "2020-05-32\n" "2020-06-31\n" "2020-07-32\n" "2020-08-32\n" "2020-09-31\n" "2020-10-32\n" "2020-11-31\n" "2020-12-32\n" "a222-01-01\n" "2a22-01-01\n" "22a2-01-01\n" "222a-01-01\n" "2222-a1-01\n" "2222-0a-01\n" "2222-1a-01\n" "2222-01-a1\n" "2222-01-0a\n" "2222-01-1a") matches = regex.finditer(test_str) for match_num, match in enumerate(matches, start=1): print(f"Match {match_num} was found at {match.start()}-{match.end()}: {match.group()}") for group_num, group in enumerate(match.groups(), start=1): print(f"Group {group_num} found at {match.start(group_num)}-{match.end(group_num)}: {group}")

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