Searching and replacing text in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of simple string replace

What is the output of this Python code?

Python

text = "I love apples and apples are sweet."
result = text.replace("apples", "oranges", 1)
print(result)

A I love oranges and apples are sweet.

B I love oranges and oranges are sweet.

C I love apples and oranges are sweet.

D I love apples and apples are sweet.

💡 Hint

The replace method replaces only the first occurrence when count is 1.

The replace method replaces the first 'apples' with 'oranges'. The second 'apples' remains unchanged.

❓ Predict Output

intermediate

Replacing with regex pattern

What is the output of this code using regex substitution?

Python

import re
text = "Call me at 123-456-7890 or 987-654-3210."
result = re.sub(r"\d{3}-\d{3}-\d{4}", "[phone]", text)
print(result)

A Call me at [phone] or 987-654-3210.

B Call me at 123-456-7890 or 987-654-3210.

C Call me at [phone] or [phone].

D Call me at 123-456-7890 or [phone].

💡 Hint

re.sub replaces all matches by default.

The regex matches both phone numbers and replaces them with '[phone]'.

❓ Predict Output

advanced

Replacing only whole words

What is the output of this code that replaces only whole word 'cat' with 'dog'?

Python

import re
text = "The cat scattered the catalog on the cathedral floor."
result = re.sub(r"\bcat\b", "dog", text)
print(result)

A The dog scattered the catalog on the cathedral floor.

B The dog sdogtered the dogalog on the doghedral floor.

C The cat scattered the catalog on the cathedral floor.

D The dog scattered the dogalog on the doghedral floor.

💡 Hint

The \b in regex means word boundary.

Only the exact word 'cat' is replaced, not parts of other words.

❓ Predict Output

advanced

Replacing with a function in re.sub

What is the output of this code that replaces digits with their squares?

Python

import re
text = "Numbers: 2, 3, and 4."
def square(match):
    num = int(match.group())
    return str(num * num)
result = re.sub(r"\d", square, text)
print(result)

A Numbers: 2, 3, and 4.

B Numbers: 4, 9, and 16.

C Numbers: 4, 9, and 4.

D Numbers: 4, 3, and 16.

💡 Hint

The function is called for each digit and returns its square as string.

Each digit is replaced by its square: 2->4, 3->9, 4->16.

🧠 Conceptual

expert

Effect of overlapping patterns in re.sub

Given the code below, what is the output?

Python

import re
text = "aaaa"
result = re.sub(r"aa", "b", text)
print(result)

A ba

B aaaa

C bba

D bb

💡 Hint

re.sub does not replace overlapping matches.

The pattern 'aa' matches twice non-overlapping: positions 0-1 and 2-3, replaced by 'b' each time, resulting in 'bb'.