A tiny introduction to regular expressions in Python

1. Import the module: import re

2. Basic match: re.search(r'cat', 'concatenate') → finds 'cat' anywhere.

3. Full match: re.fullmatch(r'cat', 'cat') → must match the entire string.

4. Find all: re.findall(r'\d+', 'a1b22c333') → ['1', '22', '333']

5. Replace: re.sub(r'\s+', ' ', 'too many spaces') → 'too many spaces'

6. Character classes:

   • \d digits, \w word chars, \s whitespace
   • . any char except newline

7. Quantifiers:

   • + one or more, * zero or more, ? optional, {n,m} range

8. Anchors: ^ start, $ end, \b word boundary

9. Groups:

   • re.search(r'(ha)+', 'hahaha').group(1) → 'ha'
   • Named: (?P<name>pattern)

10. Raw strings: Always use r'pattern' to avoid problems with escaping.