How to use regex in Python

Python's re module: import re. Key functions: re.search(pattern, string) returns the first match or None. re.match(pattern, string) matches only at the start. re.findall(pattern, string) returns all matches as a list. re.sub(pattern, replacement, string) replaces matches. re.compile(pattern) creates a reusable pattern object. Always use raw strings for patterns: re.search(r'\d+', text) — the r prefix prevents Python from interpreting backslashes before the regex engine sees them.

# Python — regular expressions with re module
import re

text = "Contact us at support@example.com or sales@example.com"

# Find all email addresses
emails = re.findall(r"[\w.+-]+@[\w-]+\.[\w.]+", text)
print(emails)  # ["support@example.com", "sales@example.com"]

# Search for first match
match = re.search(r"(\w+)@(\w+\.\w+)", text)
print(match.group(1))  # "support"
print(match.group(2))  # "example.com"

# Replace with regex
cleaned = re.sub(r"[\w.+-]+@[\w-]+\.[\w.]+", "[REDACTED]", text)
print(cleaned)  # "Contact us at [REDACTED] or [REDACTED]"

# Compile for reuse
pattern = re.compile(r"^\d{3}-\d{4}$")
print(pattern.match("555-1234"))  # Match object

Python regex vs JavaScript regex differences

Most patterns work identically in Python and JavaScript. Key differences: Python supports named groups with (?P<name>...) while JavaScript uses (?<name>...) — both syntaxes work in Python 3.6+. Python has re.VERBOSE (x flag) for commented patterns. Python supports lookbehind assertions of variable length; JavaScript requires fixed-length. Python's re.split() keeps captured groups in the result; JavaScript's String.split() does the same. The \b, \d, \w, \s character classes work the same in both. Test your pattern here — if it works in this tester, it will work in Python with minimal changes.

Common Python regex patterns

Email: r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'. URL: r'https?://[^\s]+'. IP address: r'\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b'. Phone: r'\+?1?[-.\s]?\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}'. Date (YYYY-MM-DD): r'\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])'. Python variable: r'[a-zA-Z_][a-zA-Z0-9_]*'. For production email validation, use a library — regex alone cannot fully validate RFC 5322 email addresses.