Regular Expressions 101

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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"\b(4[0-9]{3}[ -])([0-9]{4}[ -]){2}[0-9]\b|\b4[0-9][0-9]{11}\b|\b(4[0-9]{3}[ -])([0-9]{4}[ -]){2}(?:[0-9]{4})?$\b|\b4[0-9][0-9]{14}\b|\b(4[0-9]{3}[ -])([0-9]{4}[ -]){3}(?:[0-9]{3})?$\b|\b4[0-9][0-9]{17}\b", flags=re.MULTILINE) test_str = ("Visa\n\n" "Requirements: Visa numbers start with the number 4 and have either 13, 16, or 19 digits (new cards).\n\n" "Pattern Parts:\n" "Starts with number 4 and 13 length:\n" "1) \\b(4[0-9]{3}[ -])([0-9]{4}[ -]){2}[0-9]\\b|\\b4[0-9][0-9]{11}\\b\n\n" "Starts with number 4 and 16 length:\n" "2) \\b(4[0-9]{3}[ -])([0-9]{4}[ -]){2}(?:[0-9]{4})?$\\b|\\b4[0-9][0-9]{14}\\b\n\n" "Starts with number 4 and 19 length:\n" "3) \\b(4[0-9]{3}[ -])([0-9]{4}[ -]){3}(?:[0-9]{3})?$\\b|\\b4[0-9][0-9]{17}\\b\n\n" "Combining 1-3 to form one pattern:\n" "\\b(4[0-9]{3}[ -])([0-9]{4}[ -]){2}[0-9]\\b|\\b4[0-9][0-9]{11}\\b|\\b(4[0-9]{3}[ -])([0-9]{4}[ -]){2}(?:[0-9]{4})?$\\b|\\b4[0-9][0-9]{14}\\b|\\b(4[0-9]{3}[ -])([0-9]{4}[ -]){3}(?:[0-9]{3})?$\\b|\\b4[0-9][0-9]{17}\\b\n\n\n" "Test Cases:\n" "Positive (should fire):\n" "13 length, no space, start with 4 Here is the cc: 4123123412341 Thanks.\n" "13 length, dashes, start with 4 4123-1234-1234-1\n" "13 length, spaces, start with 4 4123 1234 1234 1\n\n" "16 length, no space, start with 4 4221123412341234\n" "16 length, dashes, start with 4 4221-1234-1234-1234\n" "16 length, spaces, start with 4 4221 1234 1234 1234\n\n" "19 length, no space, start with 4 4241123412341234123\n" "19 length, dashes, start with 4 4241-1234-1234-1234-123\n" "19 length, spaces, start with 4 4241 1234 1234 1234-123\n\n" "Embedded in sentence with space:\n" "13 length, no space, start with 4 Here is the cc: 4123123412341\n" "13 length, dashes, start with 4 Here is the cc: 4123-1234-1234-1\n" "13 length, spaces, start with 4 Here is the cc: 4123 1234 1234 1\n\n" "16 length, no space, start with 4 Here is the cc: 4221123412341234\n" "16 length, dashes, start with 4 Here is the cc: 4221-1234-1234-1234\n" "16 length, spaces, start with 4 Here is the cc: 4221 1234 1234 1234\n\n" "19 length, no space, start with 4 Here is the cc: 4241123412341234123\n" "19 length, dashes, start with 4 Here is the cc: 4241-1234-1234-1234-123\n" "19 length, spaces, start with 4 Here is the cc: 4241 1234 1234 1234-123\n\n" "13 length, no space, start with 4 Here is the card#:4123123412341\n" "13 length, dashes, start with 4 Here is the card#:4123-1234-1234-1\n" "13 length, spaces, start with 4 Here is the card#:4123 1234 1234 1\n\n" "16 length, no space, start with 4 Here is the card#:4221123412341234\n" "16 length, dashes, start with 4 Here is the card#:4221-1234-1234-1234\n" "16 length, spaces, start with 4 Here is the card#:4221 1234 1234 1234\n\n" "19 length, no space, start with 4 Here is the card#:4241123412341234123\n" "19 length, dashes, start with 4 Here is the card#:4241-1234-1234-1234-123\n" "19 length, spaces, start with 4 Here is the card#:4241 1234 1234 1234-123\n\n" "Negative (should not fire):\n" "13 length, no space, not start with 4 0123123412341\n" "13 length, dashes, not start with 4 0123-1234-1234-1\n" "13 length, spaces, not start with 4 0123 1234 1234 1\n\n" "16 length, no space, not start with 4 0221123412341234\n" "16 length, dashes, not start with 4 0221-1234-1234-1234\n" "16 length, spaces, not start with 4 0221 1234 1234 1234\n\n" "19 length, no space, not start with 4 0241123412341234123\n" "19 length, dashes, not start with 4 0241-1234-1234-1234-123\n" "19 length, spaces, not start with 4 0241 1234 1234 1234-123\n\n" "13 length, no space, start with 4, embedded Credit Card Number4123123412341\n" "13 length, dashes, start with 4, malformed 412-31234-12341\n" "13 length num matching pattern but embedded User ID: 0000004123123412341000000 \n" "16 length, no space, start with 4, embedded Credit Card Number4123123412341234\n" "16 length, dashes, start with 4, malformed 412-312-34123-41234\n" "16 length num matching pattern but embedded User ID: 0000004123123412341234000000\n\n" "19 length, no space, start with 4, embedded Credit Card Number4123123412341234123\n" "19 length, dashes, start with 4, malformed 412-312341-234123-4123\n" "19 length num matching pattern but embedded User ID: 0000004123123412341234123000000\n\n\n") 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