Regular Expressions 101

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  • 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
  • A character except: a, b or c
  • A character in the range: a-z
  • A character not in the range: a-z
  • A character in the range: a-z or A-Z
  • Any single character
  • Alternate - match either a or b
  • Any whitespace character
  • Any non-whitespace character
  • Any digit
  • Any non-digit
  • Any word character
  • Any non-word character
  • Match everything enclosed
  • Capture everything enclosed
  • Zero or one of a
  • Zero or more of a
  • One or more of a
  • Exactly 3 of a
  • 3 or more of a
  • Between 3 and 6 of a
  • Start of string
  • End of string
  • A word boundary
  • Non-word boundary

Regular Expression
No Match


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"(?:^|\b)(?<number>(?:\d+|\d{1,3}(?:,\d{3})+)(?:\.\d+)?)(?<replace> ?|&[^;]{2,7};)(?<dimensions>(?<mathjax>\$[^\n\$]+\$)|(?<unit>(?<si>(?!as)(?:[QRYZEPTGMkhdcmµnpfazyrq]|da)?(?:mol|cd|Hz|Pa|Wb|lm|lx|Bq|Gy|Sv|kat|[mgsAKNJWCVFΩSTHL]))|(?<imperial>mil|P|in|ft|yd|mi|le|ftm|nmi|oz|lbs?|t|tsp|tbsp|c|fl oz|pt|qt|gal|(?:sq|cu) ?(?:in|ft|yd|mi)|ft-lbf?|lbf?-ft|deg|Btu|psi|Ly)|(?<common>mph|kph|rad|sr)|(?<binary>(?:(?:[KMGTPEZY])i?)?B)))(?=\b|$| |[.,:;()\[\]{}=/*+—–-])" test_str = ("I have a 30 $m^2$ pumpernickle\n" "More precisely it's 29.87$m^2$.\n" "Traveling over 4,000 km, to where once there was\n" " the year 2016 as a new method of...\n" "He crashed at 50mph\n" "They collided at speeds of over 200m/s\n" "The reading is 2kHz.\n" "The range is 20kHz–1MHz (1,000.3 kHz).\n" "Just 4M words at 30MB.") subst = "$<number>&#x202f;$<dimensions>" # You can manually specify the number of replacements by changing the 4th argument result = re.sub(regex, subst, test_str, 0, re.MULTILINE) if result: print (result) # 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: