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]
  • 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

/
/
gm

Test String

Code Generator

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = (r"(?x) # free-spacing mode\n" r"(?(DEFINE)\n" r" # Within this DEFINE block, we'll define many subroutines\n" r" # They build on each other like lego until we can define\n" r" # a \"big number\"\n\n" r" (?<one_to_9> \n" r" # The basic regex:\n" r" # one|two|three|four|five|six|seven|eight|nine\n" r" # We'll use an optimized version:\n" r" # Option 1: four|eight|(?:fiv|(?:ni|o)n)e|t(?:wo|hree)|\n" r" # s(?:ix|even)\n" r" # Option 2:\n" r" (?:f(?:ive|our)|s(?:even|ix)|t(?:hree|wo)|(?:ni|o)ne|eight)\n" r" ) # end one_to_9 definition\n\n" r" (?<ten_to_19> \n" r" # The basic regex:\n" r" # ten|eleven|twelve|thirteen|fourteen|fifteen|sixteen|seventeen|\n" r" # eighteen|nineteen\n" r" # We'll use an optimized version:\n" r" # Option 1: twelve|(?:(?:elev|t)e|(?:fif|eigh|nine|(?:thi|fou)r|\n" r" # s(?:ix|even))tee)n\n" r" # Option 2:\n" r" (?:(?:(?:s(?:even|ix)|f(?:our|if)|nine)te|e(?:ighte|lev))en|\n" r" t(?:(?:hirte)?en|welve)) \n" r" ) # end ten_to_19 definition\n\n" r" (?<two_digit_prefix>\n" r" # The basic regex:\n" r" # twenty|thirty|forty|fifty|sixty|seventy|eighty|ninety\n" r" # We'll use an optimized version:\n" r" # Option 1: (?:fif|six|eigh|nine|(?:tw|sev)en|(?:thi|fo)r)ty\n" r" # Option 2:\n" r" (?:s(?:even|ix)|t(?:hir|wen)|f(?:if|or)|eigh|nine)ty\n" r" ) # end two_digit_prefix definition\n\n" r" (?<one_to_99>\n" r" (?&two_digit_prefix)(?:[- ](?&one_to_9))?|(?&ten_to_19)|\n" r" (?&one_to_9)\n" r" ) # end one_to_99 definition\n\n" r" (?<one_to_999>\n" r" (?&one_to_9)[ ]hundred(?:[ ](?:and[ ])?(?&one_to_99))?|\n" r" (?&one_to_99)\n" r" ) # end one_to_999 definition\n\n" r" (?<one_to_999_999>\n" r" (?&one_to_999)[ ]thousand(?:[ ](?&one_to_999))?|\n" r" (?&one_to_999)\n" r" ) # end one_to_999_999 definition\n\n" r" (?<one_to_999_999_999>\n" r" (?&one_to_999)[ ]million(?:[ ](?&one_to_999_999))?|\n" r" (?&one_to_999_999)\n" r" ) # end one_to_999_999_999 definition\n\n" r" (?<one_to_999_999_999_999>\n" r" (?&one_to_999)[ ]billion(?:[ ](?&one_to_999_999_999))?|\n" r" (?&one_to_999_999_999)\n" r" ) # end one_to_999_999_999_999 definition\n\n" r" (?<one_to_999_999_999_999_999>\n" r" (?&one_to_999)[ ]trillion(?:[ ](?&one_to_999_999_999_999))?|\n" r" (?&one_to_999_999_999_999)\n" r" ) # end one_to_999_999_999_999_999 definition\n\n" r" (?<bignumber>\n" r" zero|(?&one_to_999_999_999_999_999)\n" r" ) # end bignumber definition\n\n" r" (?<zero_to_9>\n" r" (?&one_to_9)|zero\n" r" ) # end zero to 9 definition\n\n" r" (?<decimals>\n" r" point(?:[ ](?&zero_to_9))+\n" r" ) # end decimals definition\n" r" \n" r") # End DEFINE\n\n\n" r"####### The Regex Matching Starts Here ########\n" r"^(?&bignumber)(?:[ ](?&decimals))?$\n\n" r"### Other examples of groups we could match ###\n" r"#(?&bignumber)\n" r"# (?&one_to_99)\n" r"# (?&one_to_999)\n" r"# (?&one_to_999_999)\n" r"# (?&one_to_999_999_999)\n" r"# (?&one_to_999_999_999_999)\n" r"# (?&one_to_999_999_999_999_999)") test_str = ("one trillion\n" "seven hundred twenty two\n" "7even\n" "zero point nine five\n" "nine hundred ninety nine thousand two hundred thirteen") matches = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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