How to Check if String Matches Pattern in Python

In Python, use the re module's match() or search() functions to check if a string matches a pattern. The match() function checks from the start of the string, while search() looks anywhere in the string.

Syntax

Use the re module functions to check patterns in strings:

• re.match(pattern, string): Checks if the string starts with the pattern.
• re.search(pattern, string): Checks if the pattern appears anywhere in the string.
• pattern is a regular expression describing the pattern.
• Returns a match object if found, otherwise None.

python

import re

match_obj = re.match(r'pattern', 'string to check')
search_obj = re.search(r'pattern', 'string to check')

Example

This example shows how to check if a string starts with 'Hello' and if it contains 'world' anywhere.

python

import re

text = 'Hello, world!'

# Check if string starts with 'Hello'
if re.match(r'Hello', text):
    print('String starts with Hello')
else:
    print('String does not start with Hello')

# Check if string contains 'world' anywhere
if re.search(r'world', text):
    print('String contains world')
else:
    print('String does not contain world')

Output

String starts with Hello
String contains world

Common Pitfalls

Common mistakes when checking string patterns include:

• Using re.match() when you want to find a pattern anywhere in the string (use re.search() instead).
• Not using raw strings (r'') for patterns, which can cause errors with backslashes.
• Assuming re.match() returns True or False instead of a match object or None.

python

import re

text = 'Say hello to the world'

# Wrong: re.match looks only at start
if re.match(r'world', text):
    print('Found world at start')
else:
    print('Did not find world at start')

# Right: use re.search to find anywhere
if re.search(r'world', text):
    print('Found world anywhere')
else:
    print('Did not find world anywhere')

Output

Did not find world at start
Found world anywhere

Quick Reference

Function	Description	Returns
re.match(pattern, string)	Checks if string starts with pattern	Match object or None
re.search(pattern, string)	Checks if pattern appears anywhere in string	Match object or None
match_obj.group()	Gets matched text from match object	Matched substring
re.fullmatch(pattern, string)	Checks if entire string matches pattern	Match object or None

Key Takeaways

Use re.match() to check if a string starts with a pattern.

Use re.search() to find a pattern anywhere in the string.

Always use raw strings (r'') for regex patterns to avoid errors.

re.match() and re.search() return match objects, not booleans.

Use re.fullmatch() to check if the whole string matches the pattern.