Podcast
Questions and Answers
What are character classes in regular expressions?
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?
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?
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?
What do the pattern [1-5] and [0-9] represent?
What happens when you place a ^ at the start of a character class?
What happens when you place a ^ at the start of a character class?
Other metacharacters such as $ and . have meaning within character classes.
Other metacharacters such as $ and . have meaning within character classes.
What does the pattern [^A-Z] do?
What does the pattern [^A-Z] do?
Fill in the blanks to match strings that are not entirely composed of digits: import re pattern = r'[0-9'
Fill in the blanks to match strings that are not entirely composed of digits: import re pattern = r'[0-9'
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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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