Searching and replacing text in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What Python method is commonly used to replace parts of a string?

The str.replace(old, new) method is used to replace occurrences of old substring with new substring in a string.

beginner

How do you search for a substring inside a string in Python?

You can use the in keyword or the str.find() method. in returns True or False, while find() returns the index or -1 if not found.

intermediate

What does str.replace('a', 'b', 1) do?

It replaces only the first occurrence of 'a' with 'b' in the string. The third argument limits the number of replacements.

intermediate

Why might you use the re.sub() function instead of str.replace()?

re.sub() allows replacing text using patterns (regular expressions), which is more powerful for complex searching and replacing.

beginner

What will this code output?

text = 'apple apple apple'
print(text.replace('apple', 'orange', 2))

It will output: orange orange apple because only the first two 'apple' words are replaced.

Which method replaces all occurrences of a substring in Python?

A str.split(separator)

B str.replace(old, new)

C str.index(substring)

D str.find(substring)

str.replace() replaces all occurrences of old with new.

What does str.find(substring) return if the substring is not found?

A -1

B 0

C None

D Raises an error

str.find() returns -1 if the substring is not found.

How can you replace only the first occurrence of a substring in Python?

A Use <code>str.split()</code>

B Use <code>str.replace(old, new)</code>

C Use <code>str.find()</code>

D Use <code>str.replace(old, new, 1)</code>

The third argument in str.replace() limits the number of replacements.

Which Python module provides advanced searching and replacing with patterns?

A re

B os

C sys

D math

The re module supports regular expressions for pattern matching.

What will this code print?

text = 'cat dog cat'
print(text.replace('cat', 'fox', 1))

A cat dog fox

B fox dog fox

C fox dog cat

D cat dog cat

Only the first 'cat' is replaced with 'fox'.

Explain how to search for a substring and replace it in a Python string.

Think about how to check if text exists and then how to change it.

Describe when and why you would use the re.sub() function instead of str.replace().

Consider cases where simple text replacement is not enough.