Python Regular Expressions Exercises With Answers

What does re.search return when no match is found?

1. Nonecorrect
2. An empty string
3. False
4. An empty list

Answer: None

Why: A failed search returns None, so check the result before calling group().

What is the output?

import re
print(re.findall(r"\d", "a1b2"))

1. ['1', '2']correct
2. [1, 2]
3. '12'
4. ['a', 'b']

Answer: ['1', '2']

Why: The pattern matches one digit at a time, and findall returns strings.

What does the pattern r"\d+" match?

1. One or more letters
2. One or more digitscorrect
3. One digit only
4. A literal backslash

Answer: One or more digits

Why: \d means a digit and + means one or more repetitions.

What does this code print?

import re
print(re.sub(r"cat", "dog", "cat cat"))

1. dog dogcorrect
2. cat dog
3. cat cat
4. dog cat

Answer: dog dog

Why: re.sub replaces every occurrence of cat with dog.

Complete the import.

____ re
print(re.findall(r"\d+", "a1"))

Answer: import

Why: The re module must be imported before its functions are used.

Complete the pattern that finds digit groups.

import re
text = "a1b22"
print(re.findall(r"____+", text))

Answer: \d

Why: The pattern \d+ matches one or more digits.

Complete the replacement function.

import re
print(re.____(r"cat", "dog", "cat"))

Answer: sub

Why: re.sub replaces matching parts of a string.

Complete the search call.

import re
print(re.____(r"\d+", "a1").group())

Answer: search

Why: re.search returns the first match, and group() reads its text.

What does the program output?

import re
print(re.findall(r"\d+", "a1b22")[1])

Answer: 22

Why: The matches are ['1', '22'], so index 1 is 22.

What appears on the screen?

import re
print(re.sub(r"\s+", "-", "a  b"))

Answer: a-b

Why: The repeated spaces become one hyphen, producing a-b.

What is printed?

import re
print(bool(re.search(r"\d", "abc")))

Answer: False

Why: There is no digit in abc, so search returns None and bool(None) is False.

What is the output?

import re
print(re.findall(r"[A-Z]", "pyTHON"))

Answer: ['T', 'H', 'O', 'N']

Why: The uppercase letters are T, H, O, and N.