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Quiz: Text Processing and Regular Expressions

Test your understanding of regular expressions, the re module, pattern elements, quantifiers, and text substitution with these questions. Click "Show Answer" to reveal the correct answer and explanation.

1. What Python module provides regular expression functions?

  1. import regex
  2. import pattern
  3. import re
  4. import text
Show Answer

The correct answer is C. Python's standard library includes the re module for regular expressions. Import it with import re. The main functions are re.search(), re.findall(), re.split(), and re.sub(). Regular expressions are patterns you write to search, match, split, or replace text in powerful ways that would take many lines of string methods to replicate.

Concept Tested: re Module

2. Why should you use raw strings (r"...") for regex patterns?

  1. Raw strings run faster because Python skips the string parser
  2. Raw strings prevent Python from interpreting backslashes as escape sequences, so regex characters like \d are passed literally to the regex engine
  3. Raw strings are required for multi-line patterns to work correctly
  4. Raw strings automatically make the pattern case-insensitive
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The correct answer is B. Regex patterns use many backslash sequences: \d for digit, \w for word character, \s for whitespace. In a normal Python string, backslash starts escape sequences (\n = newline). A raw string (r"...") tells Python not to process backslashes, so r"\d" passes \d literally to the regex engine. Always use r"..." for regex patterns.

Concept Tested: Raw Strings for Regex

3. What does the regex pattern \d match?

  1. Any letter (a-z or A-Z)
  2. Any whitespace character (space, tab, newline)
  3. Any single digit (0-9)
  4. Any word character (letter, digit, or underscore)
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The correct answer is C. \d matches any single digit character from 0 to 9. To match a word character (letters, digits, underscore), use \w. To match whitespace, use \s. The uppercase versions (\D, \W, \S) match the opposite — anything that is NOT a digit, word character, or whitespace, respectively.

Concept Tested: Pattern Elements

4. What does re.search(r"\d{3}-\d{4}", "Call 555-1234!") return?

  1. True
  2. The string "555-1234"
  3. A match object (because the pattern was found in the text)
  4. None (because the text is not entirely a phone number)
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The correct answer is C. re.search() returns a match object if the pattern is found anywhere in the text, or None if not found. It does not return a simple boolean or the matched text directly. To get the actual matched string, call .group() on the match object: match.group() would return "555-1234".

Concept Tested: re.search()

5. What does the quantifier + mean in a regex pattern?

  1. Match the preceding element exactly one time
  2. Match the preceding element one or more times
  3. Match the preceding element zero or one time (making it optional)
  4. Match the preceding element zero or more times
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The correct answer is B. The + quantifier means "one or more times" — the preceding element must appear at least once. For example, \d+ matches one or more digits: it matches "5", "42", "1000" but NOT an empty string. Compare: * means zero or more (can be absent), ? means zero or one (optional), {n} means exactly n times.

Concept Tested: Quantifiers

6. What does re.findall(r"\d+", "I have 3 cats and 12 fish") return?

  1. "3" (only the first number found)
  2. None
  3. ["3", "12"] (a list of all matches)
  4. 2 (the count of matches)
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The correct answer is C. re.findall() returns a list of all non-overlapping matches as strings. For \d+ (one or more digits) applied to "I have 3 cats and 12 fish", it finds "3" and "12" and returns them as ["3", "12"]. Unlike re.search() which stops at the first match, findall() collects all occurrences.

Concept Tested: re.findall()

7. What does re.sub(r"\s+", "-", "hello world foo") produce?

  1. "hello world foo" (unchanged, because sub only works with exact matches)
  2. "hello-world-foo"
  3. ["hello", "world", "foo"]
  4. "hello-world foo" (only the first match is replaced)
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The correct answer is B. re.sub(pattern, replacement, text) replaces all matches of the pattern with the replacement string. \s+ matches one or more whitespace characters. The single space between "hello" and "world" and the double space between "world" and "foo" are both replaced by "-", giving "hello-world-foo". By default, re.sub() replaces all occurrences.

Concept Tested: re.sub()

8. What does the ^ anchor do in a regex pattern?

  1. Matches any character except newline
  2. Marks the end of the pattern to match
  3. Makes the pattern case-insensitive
  4. Requires the pattern to match at the start of the string
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The correct answer is D. The ^ anchor asserts that the match must occur at the beginning of the string. For example, r"^\d" matches strings that start with a digit. Without ^, re.search(r"\d", text) finds a digit anywhere in the text. The $ anchor similarly requires the match to be at the end of the string. Together, ^...$ matches the entire string.

Concept Tested: Anchors

9. What does re.split(r",\s*", "apples, oranges,bananas, grapes") return?

  1. "apples oranges bananas grapes" (all commas removed)
  2. ["apples", "oranges", "bananas", "grapes"]
  3. ["apples, oranges", "bananas, grapes"]
  4. 4 (the number of items)
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The correct answer is B. re.split(pattern, text) splits the text at every match of the pattern, returning a list of the pieces. The pattern r",\s*" matches a comma followed by zero or more whitespace characters, handling all the different spacing styles around commas. The result is a clean list: ["apples", "oranges", "bananas", "grapes"].

Concept Tested: re.split()

10. What does the . character match in a regular expression?

  1. Only a literal period character
  2. Any single character except a newline
  3. Any digit or letter (but not punctuation)
  4. Zero or more of the preceding character
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The correct answer is B. In a regex, . is a wildcard that matches any single character except a newline (\n). For example, r"c.t" would match "cat", "cut", "c4t", and "c!t". To match a literal period, escape it: r"\.". The quantifiers * and + control repetition — they are not matched by ..

Concept Tested: Pattern Elements