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"
"
xmg

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""" (?ms)^\d+\.\s*(.*?)(?=^\d+\.|\Z) """ test_str = ("5. What ultrasound finding in a breast lesion is typically associated with malignancy?\n" "A. Increased through transmission\n" "B. Height greater than width\n" "C. Hyperechogenicity\n" "D. Surrounding hyperechoic halo\n" "Key: B Rationale: A. Incorrect. Increased through transmission is typically associated with benign simple cysts. B. Correct. Height greater than width is a sonographic feature that is typically associated with malignancy. C. Incorrect. Hyperechogenicity typically is seen with benign fat containing lesions and is not a typical feature of malignancy. D. Incorrect. A surrounding hyperechoic (echogenic) halo is typically associated with benign post traumatic findings.\n" "References: Stavros AT. Breast Ultrasound. Lippincott Williams and Wilkins, 2004. P. 472.\n\n" "6. For which ONE of the following would a BIRADS 6 classification be MOST appropriate?\n" "A. Post procedure mammogram for marker placement\n" "B. Prior treated breast cancer\n" "C. Recent biopsy proven breast cancer\n" "D. Suspicious abnormality; needs biopsy\n" "Key: C\n" "Rationale: A. Incorrect. A Birads category is not given on the post procedure mammogram for marker placement. B. Incorrect. Patients with a history of breast cancer are not assigned a Birads Category 6, which is reserved for patients with known (untreated as yet) malignancy. C. Correct. Birads Category 6 is assigned to patients with a diagnosis of cancer who have not yet been definitively treated. D. Incorrect. Patients with suspicious abnormalities; need biopsy should be coded Birads Category 4. Birads 6 is reserved for patients with a known biopsy proven diagnosis of breast cancer.\n" "References: ACR BIRADS Atlas, 5th Edition, 2013. P. 149-159.") matches = re.finditer(regex, test_str, re.VERBOSE | 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