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
No Match

r"
"
gm

Test String

Code Generator

Language

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"^[\s]{0,2}\[([\d]*)\]:" test_str = ("---\n" " # Meta Data\n" " Title: Test Set for Mark Down Reference Linking\n" " Summary: Test Set for Mark Down Reference Linking\n" " Author: Royi \n\n" " # Settings\n" " settings:\n" " enable_uml: true\n" " image_path_conversion: base64\n" " markdown_extensions:\n" " - markdown.extensions.footnotes\n" " - markdown.extensions.fenced_code\n" " - markdown.extensions.tables\n" " - markdown.extensions.admonition\n" " - markdown.extensions.toc:\n" " title: Table of Contents\n" " toc_depth: 2-3\n" " - pymdownx.arithmatex:\n" " generic: true\n" " smart_dollar: false\n" " allow_css_overrides: true\n" "---\n\n\n" "# Test Set for Mark Down Reference Linking\n\n" "[TOC]\n\n" "## Scope of the Document\n\n" "Just some text as a test set.\n\n\n" "### Some ASCII Graphics\n\n" "Laser beam.\n\n" "```\n" " \n" " Target \n" " \n" " +--------------------------------+ \n" " | | \n" " | | \n" " | | \n" " | | \n" " | -- | \n" " | -/ | \n" " | --/ | \n" " | -/ | \n" " | --/ | \n" " +--------------------------------+ \n" " -/ \n" " --/ \n" " <-------------------/-----------------------> \n" " --/ \n" " -/ \n" " --/ \n" " +--------/ \n" " | -/| \n" " | -/ | \n" " | | Laser Beam\n" " +------+ \n" "```\n\n" "## Some List\n\n" " * Train Set - Set used for training the ML model (For instance optimize the model parameters [For Parametric Model])\n" " * Test Set - Set used to evaluate results.\n" " * Prediction - Prediction of velocity given a measurement.\n\n" "Implicit / Explicit Assumptions[^001]:\n\n" " * The laser beam is eye safe.\n" " * Just some information[^002].\n\n" "### Some Existing Links\n\n" "The results are pretty good in [RMSE][001] / [MAE][002].\n\n\n" "## Some Text to Test\n\n" "Free text, **bold text**, *italic text*, [__bold text__][003] or _italic text_.\n" "Also, `Mono Spaced Text` and regular [boring text][04].\n\n" "Some [Link](https://www.wikipedia.com) and [Reference Link][1].\n\n" "Some list...\n\n" " * Examining Deep Learning (DL) Based Methods \n" " Always some text on [Deep][1] Learning.\n" " * Hyper Parameters \n" " Adding an exhaustive search of the optimal Hyper Parameters.\n\n\n" " [001]: https://en.wikipedia.org/wiki/Root-mean-square_deviation \"Wikipedia - RMSE\"\n" " [002]: https://en.wikipedia.org/wiki/Mean_absolute_error \"Wikipedia - MAE\"\n\n" "[003]: https://something.com\n" " [04]: https://somewhere.com\n\n" " [5]: Should not be selected!\n" " [6]: Should not be selected!\n\n\n" " [^001]: Just a simple assumption reference.\n" " [^002]: Just another simple assumption reference.\n\n\n\n\n" "[1]: https://www.wikipedia.com") 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