🚀 *Gen AI Engineer Telugu (Production Focused)* Basic Character Classes
| Pattern | Description | Example Matches |
|---|---|---|
[abc] | Matches any single character in the brackets | a, b, or c |
[^abc] | Matches any single character NOT in the brackets | d, 1, ! (not a, b, or c) |
[a-z] | Matches any character in the range a to z | a, b, c, …, z |
[A-Z] | Matches any character in the range A to Z | A, B, C, …, Z |
[0-9] | Matches any digit | 0, 1, 2, …, 9 |
[a-zA-Z] | Matches any letter (lowercase or uppercase) | a, B, z, Y |
[a-z0-9] | Matches any lowercase letter or digit | a, 5, z, 9 |
[A-Z0-9] | Matches any uppercase letter or digit | A, 5, Z, 9 |
1. [abc] – Matches any single character in the brackets
Description: Matches exactly one character that is either ‘a’, ‘b’, or ‘c’
Example 1: Find vowels in a word
python
import re text = "hello world" result = re.findall(r'[aeiou]', text) print(result) # ['e', 'o', 'o'] # Matches all vowels in the text
Example 2: Find specific punctuation
python
text = "Hello! How are you? I'm fine." result = re.findall(r'[!?.]', text) print(result) # ['!', '?', '.'] # Matches specific punctuation marks
Example 3: Find digits 1, 2, or 3
python
text = "Phone: 123-456-7890" result = re.findall(r'[123]', text) print(result) # ['1', '2', '3'] # Matches only digits 1, 2, and 3
Example 4: Find specific letters (case-sensitive)
python
text = "Apple Banana cherry" result = re.findall(r'[AB]', text) print(result) # ['A', 'B'] # Matches only uppercase A and B
2. [^abc] – Matches any single character NOT in the brackets
Description: Matches any character except ‘a’, ‘b’, or ‘c’
Example 1: Find non-vowels
python
text = "hello world" result = re.findall(r'[^aeiou]', text) print(result) # ['h', 'l', 'l', ' ', 'w', 'r', 'l', 'd'] # All characters except vowels
Example 2: Find non-digits
python
text = "Room 101, Floor 2" result = re.findall(r'[^0-9]', text) print(result) # ['R', 'o', 'o', 'm', ' ', ',', ' ', 'F', 'l', 'o', 'o', 'r', ' '] # All characters except digits
Example 3: Exclude specific punctuation
python
text = "Hello! How are you? I'm fine, thanks."
result = re.findall(r'[^!?,]', text)
print(''.join(result)) # "Hello How are you I'm fine thanks."
# All characters except !, ?, and ,
Example 4: Exclude specific letters
python
text = "abcxyz123" result = re.findall(r'[^abc]', text) print(result) # ['x', 'y', 'z', '1', '2', '3'] # All characters except a, b, and c
3. [a-z] – Matches any character in the range a to z
Description: Matches any lowercase letter from a to z
Example 1: Find all lowercase letters
python
text = "Hello World 123" result = re.findall(r'[a-z]', text) print(result) # ['e', 'l', 'l', 'o', 'o', 'r', 'l', 'd'] # All lowercase letters
Example 2: Find lowercase words
python
text = "Python is AWESOME for coding" result = re.findall(r'[a-z]+', text) print(result) # ['ython', 'is', 'for', 'coding'] # Lowercase words (note: 'Python' becomes 'ython' because P is uppercase)
Example 3: Validate username (lowercase only)
python
username = "john_doe123" is_valid = bool(re.fullmatch(r'[a-z0-9_]+', username)) print(is_valid) # True # Checks if username contains only lowercase letters, digits, and underscores
Example 4: Extract file extensions (lowercase)
python
files = "image.JPG document.txt script.PY readme.md" result = re.findall(r'\.([a-z]+)', files) print(result) # ['txt', 'md'] # Only lowercase file extensions
4. [A-Z] – Matches any character in the range A to Z
Description: Matches any uppercase letter from A to Z
Example 1: Find all uppercase letters
python
text = "Hello World from PYTHON" result = re.findall(r'[A-Z]', text) print(result) # ['H', 'W', 'P', 'Y', 'T', 'H', 'O', 'N'] # All uppercase letters
Example 2: Find acronyms and abbreviations
python
text = "The USA and UK are countries. NASA is a space agency."
result = re.findall(r'[A-Z]{2,}', text)
print(result) # ['USA', 'UK', 'NASA']
# Words with 2 or more uppercase letters
Example 3: Find sentence starters
python
text = "hello. World! how are you? I am fine." result = re.findall(r'[A-Z][a-z]*', text) print(result) # ['World', 'I'] # Words that start with uppercase letter (likely sentence starters)
Example 4: Validate product codes
python
codes = ["AB123", "CD456", "ef789", "GH-001"]
valid_codes = [code for code in codes if re.fullmatch(r'[A-Z]{2}\d{3}', code)]
print(valid_codes) # ['AB123', 'CD456']
# Codes with exactly 2 uppercase letters followed by 3 digits
5. [0-9] – Matches any digit
Description: Matches any digit from 0 to 9
Example 1: Extract all digits
python
text = "Phone: 123-456-7890, Age: 25" result = re.findall(r'[0-9]', text) print(result) # ['1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '2', '5'] # All individual digits
Example 2: Find numbers with specific digits
python
text = "Scores: 95, 87, 73, 64, 59, 100" result = re.findall(r'[5-9][0-9]', text) print(result) # ['95', '87', '73', '64', '59'] # Numbers between 50-99
Example 3: Validate PIN code
python
pin = "1234"
is_valid = bool(re.fullmatch(r'[0-9]{4}', pin))
print(is_valid) # True
# 4-digit PIN code validation
Example 4: Extract years from text
python
text = "Events in 1999, 2005, 2010, and 2020"
result = re.findall(r'[12][0-9]{3}', text)
print(result) # ['1999', '2005', '2010', '2020']
# Years between 1000-2999
6. [a-zA-Z] – Matches any letter (lowercase or uppercase)
Description: Matches any letter regardless of case
Example 1: Extract all letters
python
text = "Hello World 123! @#$" result = re.findall(r'[a-zA-Z]', text) print(result) # ['H', 'e', 'l', 'l', 'o', 'W', 'o', 'r', 'l', 'd'] # All letters, ignoring case
Example 2: Find words (letters only)
python
text = "Python3 is better than Java8!" result = re.findall(r'[a-zA-Z]+', text) print(result) # ['Python', 'is', 'better', 'than', 'Java'] # Words consisting only of letters
Example 3: Validate name field
python
name = "John Doe" is_valid = bool(re.fullmatch(r'[a-zA-Z ]+', name)) print(is_valid) # True # Name containing only letters and spaces
Example 4: Extract capitalized words
python
text = "The Quick Brown Fox jumps Over The Lazy Dog" result = re.findall(r'[A-Z][a-z]*', text) print(result) # ['The', 'Quick', 'Brown', 'Fox', 'Over', 'The', 'Lazy', 'Dog'] # Words that start with uppercase letter
7. [a-z0-9] – Matches any lowercase letter or digit
Description: Matches lowercase letters or digits
Example 1: Extract alphanumeric characters (lowercase)
python
text = "User123: john_doe, Email: test@example.com" result = re.findall(r'[a-z0-9]', text) print(result) # ['s', 'e', 'r', '1', '2', '3', 'j', 'o', 'h', 'n', 'd', 'o', 'e', 'e', 's', 't', 'e', 'x', 'a', 'm', 'p', 'l', 'e', 'c', 'o', 'm'] # Lowercase letters and digits only
Example 2: Validate username (lowercase alphanumeric)
python
username = "john123" is_valid = bool(re.fullmatch(r'[a-z0-9]+', username)) print(is_valid) # True # Username with only lowercase letters and digits
Example 3: Extract hashtags (lowercase)
python
text = "#Python #coding #PROGRAMMING #java123" result = re.findall(r'#[a-z0-9]+', text) print(result) # ['#coding', '#java123'] # Lowercase hashtags with numbers
Example 4: Find version numbers
python
text = "Versions: v1.2.3, V2.5, v10.0.1" result = re.findall(r'v([a-z0-9.]+)', text, re.IGNORECASE) print(result) # ['1.2.3', '2.5', '10.0.1'] # Version numbers after 'v' (case-insensitive)
8. [A-Z0-9] – Matches any uppercase letter or digit
Description: Matches uppercase letters or digits
Example 1: Extract uppercase alphanumeric characters
python
text = "Product Code: AB123, Serial: XYZ456-789" result = re.findall(r'[A-Z0-9]', text) print(result) # ['P', 'C', 'A', 'B', '1', '2', '3', 'S', 'X', 'Y', 'Z', '4', '5', '6', '7', '8', '9'] # Uppercase letters and digits only
Example 2: Validate license plate format
python
plate = "AB123CD" is_valid = bool(re.fullmatch(r'[A-Z0-9]+', plate)) print(is_valid) # True # License plate with uppercase letters and digits
Example 3: Extract stock symbols
python
text = "Stocks: AAPL, GOOGL, MSFT, TSLA123"
result = re.findall(r'[A-Z0-9]{2,}', text)
print(result) # ['AAPL', 'GOOGL', 'MSFT', 'TSLA123']
# Uppercase stock symbols with possible numbers
Example 4: Find hexadecimal numbers (uppercase)
python
text = "Colors: #FF0000, #00FF00, #0000FF, #abcdef"
result = re.findall(r'#[A-F0-9]{6}', text)
print(result) # ['#FF0000', '#00FF00', '#0000FF']
# Uppercase hexadecimal color codes
