Python Regex Exercises: Search, Find, and Replace

Use raw strings

Write regex patterns as raw strings, such as r"\d+". The r prefix stops Python from interpreting backslashes before the regex engine sees them. This avoids a common source of confusing bugs.

import re
print(re.findall(r"\d+", "a1 b22 c333"))

Digits with a raw string

Search for one match

re.search returns a match object for the first occurrence, or None. Read the text with group(). Check for None before using the result, especially when the input comes from a user or a file.

import re
match = re.search(r"\d+", "Order 42")
if match:
    print(match.group())

Check before reading

Find all matches

re.findall returns a list of every non-overlapping match. Character classes let one pattern match a set of characters: [A-Z] finds uppercase letters. Combine classes with quantifiers to describe repetition.

import re
print(re.findall(r"[A-Z]", "pyTHON"))
print(re.findall(r"\d+", "a1 b22"))

Collect every match

Replace text

re.sub replaces every match with a replacement string. A pattern such as \s+ matches runs of whitespace. Test the replacement on a small sample before applying it to a whole document.

import re
text = "latte   tea  mocha"
print(re.sub(r"\s+", " ", text))

Normalise spacing

Validate a simple shape

re.fullmatch checks that the whole string matches the pattern. Here \d{3}-\d{4} describes three digits, a hyphen, and four digits. Return a boolean when the caller only needs to know whether the input is valid.

import re
phone = "555-1234"
print(bool(re.fullmatch(r"\d{3}-\d{4}", phone)))

A whole-string check

Your practice checklist

• Use raw strings for patterns.
• Check whether search returned None before calling group().
• Test one pattern on a small input first.
• Prefer clear character classes over clever, unreadable patterns.

Common questions

Keep reading:

• Python Regular Expressions
• Python Exercises With Answers: How to Practice Without Copying
• Python Practice for Beginners: A Simple 4-Week Plan