Python re Module Basics

The four functions you'll use 90% of the time

Python's built-in regex lives in the re module. Four functions cover most use cases:

re.search(pattern, text) — find the first match anywhere in text. Returns a Match object or None.
re.match(pattern, text) — match at the START of text only. Returns Match or None.
re.fullmatch(pattern, text) — match the ENTIRE text. Returns Match or None.
re.findall(pattern, text) — return all non-overlapping matches as a list.
re.finditer(pattern, text) — return an iterator of Match objects (preferred over findall when you have groups).

The Match object

When a pattern matches, you get a Match object with these key methods:

m.group() or m.group(0) — the entire match
m.group(N) — the Nth capture group
m.group('name') — a named capture group
m.groups() — tuple of all numbered groups
m.groupdict() — dict of all named groups
m.start(), m.end(), m.span() — match position

Match vs search — the most common confusion

re.match only checks the start of the string. re.match(r'world', 'hello world') returns None. Use re.search for "contains." Use re.match for "starts with." Use re.fullmatch for "is exactly."

Code

The Python re basics·python

import re

text = 'order #1138 placed on 2026-05-04'

# search — find anywhere
m = re.search(r'#(\d+)', text)
m.group()      # '#1138'
m.group(1)     # '1138'

# match — only at start
re.match(r'order', text)  # Match
re.match(r'placed', text)  # None

# fullmatch — the whole thing
re.fullmatch(r'\d{4}', '2026')         # Match
re.fullmatch(r'\d{4}', '2026 today')   # None

# findall — list of matches
re.findall(r'\d+', text)
# ['1138', '2026', '05', '04']

# finditer — iterator of Match objects
for m in re.finditer(r'(\w+)=(\d+)', 'a=1 b=2 c=3'):
    print(m.group(1), '→', m.group(2))
# a → 1
# b → 2
# c → 3

Python re Module Basics

The four functions you'll use 90% of the time

The Match object

Match vs search — the most common confusion

Code

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