re.match() / re.search() / re.fullmatch()

import re

# Check if the pattern matches at the beginning of the string.
m = re.match(pattern, string)

# Search the entire string for the first match.
m = re.search(pattern, string)

# Check if the entire string matches the pattern exactly.
m = re.fullmatch(pattern, string)

# Retrieve matched strings from the match object.
m.group()      # Returns the entire match.
m.group(1)     # Returns the first capture group.
m.groups()     # Returns all groups as a tuple.

import re

# match() checks from the beginning of the string.
m = re.match(r'\d+', '123abc')
if m:
    print(m.group())  # Prints '123'.

m2 = re.match(r'\d+', 'abc123')
print(m2)  # Prints 'None' because the string does not start with a digit.

# search() searches the entire string.
m3 = re.search(r'\d+', 'abc123def')
if m3:
    print(m3.group())  # Prints '123'.

# fullmatch() requires an exact match for the entire string.
m4 = re.fullmatch(r'\d+', '12345')
print(bool(m4))  # Prints 'True'.

m5 = re.fullmatch(r'\d+', '123abc')
print(bool(m5))  # Prints 'False' (contains letters in the middle).

# Use capture groups to extract parts of the match.
m6 = re.search(r'(\d{4})-(\d{2})-(\d{2})', 'Today is 2025-04-15.')
if m6:
    print(m6.group())   # Prints '2025-04-15'.
    print(m6.group(1))  # Prints '2025'.
    print(m6.group(2))  # Prints '04'.
    print(m6.groups())  # Prints "('2025', '04', '15')".

# Use named capture groups.
pattern = r'(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})'
m7 = re.search(pattern, '2025-04-15')
if m7:
    print(m7.group('year'))   # Prints '2025'.
    print(m7.group('month'))  # Prints '04'.

# Validate an email address format.
email = 'user@example.com'
if re.fullmatch(r'[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}', email):
    print('Valid email address.')

re.match() checks only the beginning of the string, while re.search() searches the entire string. Use re.search() when you want to find a pattern regardless of its position. Both functions return None on failure, so always check the return value with an if statement before accessing groups.

It is recommended to use Python raw strings (r"...") for regular expression patterns. Raw strings let you write backslashes without escaping them, making patterns easier to read.

Even when working with strings that contain Unicode characters such as Japanese, no additional configuration like PHP's /u modifier is needed — Python's regular expressions support Unicode by default.

To retrieve all matches, see re.findall() / re.finditer(). For replacement and splitting, see re.sub() / re.split() / re.compile().