Combined Character Classes Explained with Examples

1. [a-zA-Z0-9_] – Word characters (same as \w)

Description: Matches any letter (lowercase or uppercase), any digit, or underscore

Example 1: Extract all word characters from text

python

import re
text = "User_name123! Email: test@example.com"
result = re.findall(r'[a-zA-Z0-9_]', text)
print(result)  
# ['U', 's', 'e', 'r', '_', 'n', 'a', 'm', 'e', '1', '2', '3', 'E', 'm', 'a', 'i', 'l', 't', 'e', 's', 't', 'e', 'x', 'a', 'm', 'p', 'l', 'e', 'c', 'o', 'm']
# All letters, digits, and underscores

Example 2: Validate username format

python

usernames = ["john_doe123", "user-name", "Admin123", "test@user"]
valid_usernames = [user for user in usernames if re.fullmatch(r'[a-zA-Z0-9_]+', user)]
print(valid_usernames)  # ['john_doe123', 'Admin123']
# Only usernames with letters, digits, and underscores

Example 3: Extract hashtags (alphanumeric with underscore)

python

text = "#Python #coding_101 #machine-learning #AI_2024"
result = re.findall(r'#[a-zA-Z0-9_]+', text)
print(result)  # ['#Python', '#coding_101', '#AI_2024']
# Hashtags containing only word characters

Example 4: Split on non-word characters

python

text = "Hello, World! How_are_you? Test123."
words = re.findall(r'[a-zA-Z0-9_]+', text)
print(words)  # ['Hello', 'World', 'How_are_you', 'Test123']
# Extract all word sequences

2. [0-9a-fA-F] – Hexadecimal digits

Description: Matches any hexadecimal digit (0-9, a-f, A-F)

Example 1: Extract hexadecimal color codes

python

text = "Colors: #FF0000, #00ff00, #0000FF, #abc123, #XYZ999"
result = re.findall(r'#[0-9a-fA-F]{6}', text)
print(result)  # ['#FF0000', '#00ff00', '#0000FF', '#abc123']
# Valid 6-digit hex color codes

Example 2: Find hexadecimal numbers in text

python

text = "Values: 0x1A3F, 0xFF, 0xabc, 123, 0xGHI"
result = re.findall(r'0x[0-9a-fA-F]+', text)
print(result)  # ['0x1A3F', '0xFF', '0xabc']
# Hexadecimal numbers starting with 0x

Example 3: Validate MAC address format

python

mac_address = "00:1A:2B:3C:4D:5E"
is_valid = bool(re.fullmatch(r'([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}', mac_address))
print(is_valid)  # True
# Valid MAC address format

Example 4: Extract CSS color values

python

css = "color: #f00; background: #ffffff; border: #abc123; invalid: #xyz"
result = re.findall(r'#([0-9a-fA-F]{3}|[0-9a-fA-F]{6})', css)
print(result)  # ['f00', 'ffffff', 'abc123']
# 3-digit or 6-digit hex colors

3. [aeiou] – Any vowel

Description: Matches any vowel character (lowercase only in this case)

Example 1: Count vowels in text

python

text = "Hello World, how are you today?"
vowels = re.findall(r'[aeiou]', text, re.IGNORECASE)
print(vowels)  # ['e', 'o', 'o', 'o', 'a', 'e', 'o', 'u', 'o', 'a']
# All vowels (case-insensitive)
print("Total vowels:", len(vowels))  # Total vowels: 10

Example 2: Find words with multiple vowels

python

text = "Beautiful universe, rhythm sync, why try?"
result = re.findall(r'\b\w*[aeiou]\w*[aeiou]\w*\b', text, re.IGNORECASE)
print(result)  # ['Beautiful', 'universe', 'rhythm']
# Words containing at least 2 vowels

Example 3: Remove all vowels from text

python

text = "Programming is fun with Python!"
no_vowels = re.sub(r'[aeiouAEIOU]', '', text)
print(no_vowels)  # "Prgrmmng s fn wth Pythn!"
# Text with all vowels removed

Example 4: Check if word starts with vowel

python

words = ["apple", "banana", "orange", "umbrella", "hello"]
vowel_start = [word for word in words if re.match(r'^[aeiouAEIOU]', word)]
print(vowel_start)  # ['apple', 'orange', 'umbrella']
# Words starting with vowels

4. [^aeiou] – Any non-vowel

Description: Matches any character that is NOT a vowel

Example 1: Extract consonants and other characters

python

text = "Hello World! 123"
non_vowels = re.findall(r'[^aeiouAEIOU]', text)
print(non_vowels)  # ['H', 'l', 'l', ' ', 'W', 'r', 'l', 'd', '!', ' ', '1', '2', '3']
# All characters except vowels

Example 2: Find words without vowels

python

text = "sky rhythm fly why crypt my"
result = re.findall(r'\b[^aeiouAEIOU ]+\b', text)
print(result)  # ['sky', 'fly', 'why', 'crypt', 'my']
# Words that might not contain vowels (English has few of these)

Example 3: Remove vowels keeping punctuation

python

text = "Hello, World! How are you?"
result = re.sub(r'[aeiouAEIOU]', '', text)
print(result)  # "Hll, Wrld! Hw r y?"
# Text with vowels removed but punctuation preserved

Example 4: Count non-vowel characters

python

text = "Python Programming"
non_vowels = re.findall(r'[^aeiouAEIOU]', text)
print("Non-vowel characters:", len(non_vowels))  # Non-vowel characters: 12
# Count of consonants, spaces, and other non-vowels

5. [.!?] – Punctuation marks

Description: Matches period, exclamation mark, or question mark

Example 1: Find all sentence endings

python

text = "Hello! How are you? I'm fine. Great!"
punctuation = re.findall(r'[.!?]', text)
print(punctuation)  # ['!', '?', '.', '!']
# All sentence-ending punctuation

Example 2: Split text into sentences

python

text = "First sentence. Second sentence! Third sentence? Fourth one."
sentences = re.split(r'[.!?]', text)
sentences = [s.strip() for s in sentences if s.strip()]
print(sentences)  # ['First sentence', 'Second sentence', 'Third sentence', 'Fourth one']
# Text split into sentences

Example 3: Count different types of sentences

python

text = "Wow! Really? Amazing. Incredible! Is that true? Wonderful."
questions = len(re.findall(r'\?', text))
exclamations = len(re.findall(r'!', text))
statements = len(re.findall(r'\.', text))
print(f"Questions: {questions}, Exclamations: {exclamations}, Statements: {statements}")
# Questions: 2, Exclamations: 2, Statements: 2

Example 4: Validate sentence ending

python

sentences = ["Hello world.", "What's up!", "No ending", "Why not?"]
valid_ends = [s for s in sentences if re.search(r'[.!?]$', s)]
print(valid_ends)  # ["Hello world.", "What's up!", "Why not?"]
# Sentences that properly end with punctuation

6. [+-] – Plus or minus sign

Description: Matches either plus (+) or minus (-) sign

Example 1: Find mathematical operators

python

text = "5 + 3 - 2 * 4 / 1 + 6 - 0"
operators = re.findall(r'[+-]', text)
print(operators)  # ['+', '-', '+', '-']
# Only plus and minus operators (not * or /)

Example 2: Extract signed numbers

python

text = "Temperatures: +25°C, -5°C, 0°C, +30°C, -10°C"
signed_numbers = re.findall(r'[+-]\d+', text)
print(signed_numbers)  # ['+25', '-5', '+30', '-10']
# Numbers with explicit signs

Example 3: Validate mathematical expressions

python

expressions = ["5+3", "7-2", "4*1", "8/2", "9+0"]
valid_ops = [expr for expr in expressions if re.search(r'[+-]', expr)]
print(valid_ops)  # ['5+3', '7-2', '9+0']
# Expressions using only + or - operators

Example 4: Parse CSV with optional signs

python

data = "+100,-50,75,-25,+300,150"
values = re.findall(r'([+-]?\d+)', data)
print(values)  # ['+100', '-50', '75', '-25', '+300', '150']
# Numbers with optional signs
numeric_values = [int(val) for val in values]
print(numeric_values)  # [100, -50, 75, -25, 300, 150]

Bonus: Combined Examples

Example: Complex pattern using multiple character classes

python

text = "User: john_doe123, Score: +100, Email: john@example.com, Status: active"

# Extract different types of data
username = re.findall(r'User: ([a-zA-Z0-9_]+)', text)
score = re.findall(r'Score: ([+-]?\d+)', text)
email = re.findall(r'Email: ([a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,})', text)
status = re.findall(r'Status: ([a-zA-Z]+)', text)

print("Username:", username)  # ['john_doe123']
print("Score:", score)        # ['+100']
print("Email:", email)        # ['john@example.com']
print("Status:", status)      # ['active']