Regular Expressions: Character Classes Quiz
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Questions and Answers

What are character classes in regular expressions?

Characters enclosed in square brackets that represent alternate characters allowed in a pattern match.

What would [abc][def] match?

  • Any letter out of 'abc', then any out of 'def' (correct)
  • Any three letters out of 'abc', then any three from 'def'
  • Either 'abc' or 'def'
  • What would [1-5][0-9] match?

  • Any two-digit number from 10 to 59
  • 10, 19, 50, or 90 (correct)
  • Any two-digit number
  • What do the pattern [1-5] and [0-9] represent?

    <p>The first letter is from 1-5 and the second one from 0-9.</p> Signup and view all the answers

    What happens when you place a ^ at the start of a character class?

    <p>It inverts the character class.</p> Signup and view all the answers

    Other metacharacters such as $ and . have meaning within character classes.

    <p>False</p> Signup and view all the answers

    What does the pattern [^A-Z] do?

    <p>It excludes uppercase strings.</p> Signup and view all the answers

    Fill in the blanks to match strings that are not entirely composed of digits: import re pattern = r'[0-9'

    <p>^</p> Signup and view all the answers

    Study Notes

    Character Classes

    • Character classes are defined by square brackets in regular expressions, allowing the matching of alternative characters within a pattern.
    • Example: [abc] matches either 'a', 'b', or 'c'.

    Pattern Matching Examples

    • The expression [abc][def] matches any uppercase or lowercase letter in the first set followed by any letter in the second set.
    • Correct answer: C. Any letter from 'abc', followed by any letter from 'def'.

    Digit Matching Example

    • The expression [1-5][0-9] targets two-digit numbers where the first digit ranges from 1 to 5 and the second digit can be any digit from 0 to 9.
    • Correct answer: A. Matches numbers like 10, 19, 50, or 90.

    Range Values

    • For the pattern [1-5][0-9], the valid output range of numbers is between 10 and 59.
    • Min value for the first digit is 1 and max value is 5; the second digit ranges from 0 to 9.

    Inverting Character Classes

    • Placing a caret (^) at the beginning of a character class inverts the match criteria.
    • Example: [^abc] matches any character except 'a', 'b', or 'c'.

    Metacharacters in Character Classes

    • Certain metacharacters like $ and . have no functional significance when placed inside character classes.
    • They are treated as normal characters rather than special symbols.

    Excluding Uppercase Strings

    • The pattern [^A-Z] is used to exclude all uppercase letter matches, allowing everything else.

    Pattern Exclusion

    • To create a pattern that matches strings not solely composed of digits, the expression pattern = r"[^0-9]" can be utilized.
    • The caret (^) denotes exclusion when it appears at the start of a character class.

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    Description

    Test your knowledge of character classes in regular expressions with this quiz. Answer multiple-choice questions that explore how character classes work and what they match. Perfect for beginners looking to sharpen their regex skills!

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