Python Regular Expressions: re Module Complete Guide

Python Regular Expressions

Python's re module provides full PCRE support. From simple validation to complex text processing pipelines, regex is essential in every Python developer's toolkit.

import re

text = "Contact: rahul@ezycoders.in or visit https://ezycoders.in"

# search: first match anywhere
m = re.search(r'https?://[\w./]+', text)
if m: print(m.group())   # https://ezycoders.in

# findall: list of all matches
emails = re.findall(r'[\w.+-]+@[\w-]+\.[a-z]{2,}', text, re.IGNORECASE)
# ['rahul@ezycoders.in']

# sub: replace
clean = re.sub(r'\s+', ' ', "  too   many   spaces  ").strip()

# compile: reuse pattern (faster in loops)
email_pat = re.compile(r'[\w.+-]+@[\w-]+\.[a-z]{2,}', re.IGNORECASE)

Groups and Named Captures

date_pat = re.compile(r'(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})')
m = date_pat.search('Published: 2026-03-15')
if m:
    print(m.group('year'))   # '2026'
    print(m.groupdict())     # {'year':'2026','month':'03','day':'15'}

# Replace with function
result = re.sub(r'\d+', lambda m: str(int(m.group()) * 2), 'I have 5 cats')
# 'I have 10 cats'

Common Validation Patterns

PATTERNS = {
    'email':    r'^[\w.+-]+@[\w-]+\.[a-z]{2,}$',
    'phone_in': r'^[6-9]\d{9}$',
    'url':      r'^https?://[\w.-]+\.[a-z]{2,}',
    'slug':     r'^[a-z0-9]+(?:-[a-z0-9]+)*$',
    'pan_card': r'^[A-Z]{5}[0-9]{4}[A-Z]{1}$',
}

def validate(pattern_name: str, value: str) -> bool:
    pattern = PATTERNS.get(pattern_name)
    return bool(re.match(pattern, value, re.IGNORECASE))