Python Strings Complete Guide

# Creating strings
single_quote = 'Hello World'
double_quote = "Python Programming"
triple_quote = '''Multi-line
string example'''
triple_double = """Another multi-line
string example"""

# String operations
str1 = "Hello"
str2 = "Python"
concatenation = str1 + " " + str2  # "Hello Python"
repetition = str1 * 3               # "HelloHelloHello"
length = len(str1)                  # 5

# String indexing
text = "Python"
first_char = text[0]      # 'P'
last_char = text[-1]      # 'n'
third_char = text[2]      # 't'

# String slicing
substring = text[1:4]     # 'yth'
substring2 = text[:3]     # 'Pyt'
substring3 = text[3:]     # 'hon'
substring4 = text[::2]    # 'Pto' (every 2nd character)
reversed_str = text[::-1] # 'nohtyP' (reverse string)

# 1. f-strings (Python 3.6+) - RECOMMENDED
name = "Alice"
age = 25
print(f"My name is {name} and I'm {age} years old.")
# Output: My name is Alice and I'm 25 years old.

# Expressions in f-strings
a = 10
b = 20
print(f"The sum of {a} and {b} is {a + b}")
# Output: The sum of 10 and 20 is 30

# Formatting numbers
pi = 3.14159
print(f"Pi value: {pi:.2f}")  # 2 decimal places
print(f"Pi value: {pi:.4f}")  # 4 decimal places

# 2. format() method
print("My name is {} and I'm {} years old.".format(name, age))
print("My name is {1} and I'm {0} years old.".format(age, name))
print("My name is {name} and I'm {age} years old.".format(name=name, age=age))

# 3. %-formatting (older style)
print("My name is %s and I'm %d years old." % (name, age))

# 4. Advanced formatting
# Padding and alignment
print(f"{'Left':<10}")    # Left-aligned in 10 chars
print(f"{'Center':^10}")  # Center-aligned in 10 chars
print(f"{'Right':>10}")   # Right-aligned in 10 chars

# Number formatting
number = 1234.5678
print(f"{number:,}")      # 1,234.5678 (thousands separator)
print(f"{number:.2f}")    # 1234.57 (2 decimal places)
print(f"{number:10.2f}")  # Right-aligned in 10 chars, 2 decimals

# Binary, octal, hexadecimal
value = 255
print(f"Binary: {value:b}")   # 11111111
print(f"Octal: {value:o}")    # 377
print(f"Hex: {value:x}")      # ff
print(f"HEX: {value:X}")      # FF

# String concatenation
str1 = "Hello"
str2 = "World"
result = str1 + " " + str2
print(f"Concatenation: {result}")  # Hello World

# String repetition
print(f"Repetition: {'Ha' * 3}")   # HaHaHa

# String length
text = "Python Programming"
print(f"Length of '{text}': {len(text)}")  # 18

# String membership testing
print(f"'Pro' in '{text}': {'Pro' in text}")  # True
print(f"'Java' in '{text}': {'Java' in text}")  # False

# String comparison
print(f"'apple' == 'apple': {'apple' == 'apple'}")  # True
print(f"'apple' == 'Apple': {'apple' == 'Apple'}")  # False
print(f"'apple' != 'orange': {'apple' != 'orange'}")  # True

# Advanced slicing
text = "Python Programming"

# Basic slicing
print(f"text[0:6]: {text[0:6]}")      # Python
print(f"text[7:]: {text[7:]}")        # Programming
print(f"text[:6]: {text[:6]}")        # Python
print(f"text[-11:]: {text[-11:]}")    # Programming

# Step slicing
print(f"text[::2]: {text[::2]}")      # Pto rgamn (every 2nd char)
print(f"text[1::2]: {text[1::2]}")    # yhnPormig (every 2nd char starting from index 1)

# Reverse string
print(f"text[::-1]: {text[::-1]}")    # gnimmargorP nohtyP

# Negative indexing
print(f"text[-1]: {text[-1]}")        # g (last character)
print(f"text[-5:]: {text[-5:]}")      # mming (last 5 characters)

# Slicing with negative step
print(f"text[10:4:-1]: {text[10:4:-1]}")  # margo (reverse slice)

# Common string patterns
filename = "document.pdf"
# Check file extension
if filename.endswith(".pdf"):
    print(f"{filename} is a PDF file")

# Remove file extension
name_without_ext = filename.rsplit(".", 1)[0]
print(f"Filename without extension: {name_without_ext}")

# Split path
path = "/home/user/documents/file.txt"
parts = path.split("/")
print(f"Path parts: {parts}")  # ['', 'home', 'user', 'documents', 'file.txt']

# Escape sequences
print("Line 1\nLine 2")          # New line
print("Tab\tseparated")          # Tab
print("Backslash: \\")           # Backslash
print("Single quote: \'")        # Single quote
print("Double quote: \"")        # Double quote
print("Carriage return: \r")     # Carriage return
print("Backspace: Hello\bWorld") # Backspace
print("Form feed: \f")           # Form feed
print("Vertical tab: \v")        # Vertical tab
print("Octal value: \101")       # Octal (A)
print("Hex value: \x41")         # Hex (A)

# Raw strings (treat backslashes as literal)
print(r"C:\Users\Name\Documents")  # C:\Users\Name\Documents
print(r"Newline: \n won't work")   # Newline: \n won't work

# Multi-line strings
multi_line = """Line 1
Line 2
Line 3"""
print(multi_line)

# Multi-line with line continuation
long_string = ("This is a very long string that "
               "spans multiple lines using "
               "parentheses for line continuation.")
print(long_string)

# Python Strings Practice Exercises

print("=== Exercise 1: Basic String Operations ===")
# 1. Create a string with your name and print it in uppercase
name = "John Doe"
print(f"Name in uppercase: {name.upper()}")

# 2. Create a string with multiple words and count the spaces
sentence = "Python is a great programming language"
space_count = sentence.count(" ")
print(f"Spaces in sentence: {space_count}")

print("\n=== Exercise 2: String Manipulation ===")
# 3. Reverse a string without using [::-1]
text = "Python"
reversed_text = ""
for char in text:
    reversed_text = char + reversed_text
print(f"Original: {text}, Reversed: {reversed_text}")

# 4. Check if a string is palindrome
def is_palindrome(s):
    s = s.lower().replace(" ", "")
    return s == s[::-1]

test_strings = ["radar", "hello", "A man a plan a canal Panama"]
for s in test_strings:
    print(f"'{s}' is palindrome: {is_palindrome(s)}")

print("\n=== Exercise 3: String Formatting ===")
# 5. Format personal information
person = {
    "name": "Alice",
    "age": 30,
    "city": "New York",
    "salary": 75000.50
}

# Using f-string
info = f"{person['name']} is {person['age']} years old, lives in {person['city']}, and earns ${person['salary']:.2f} per year."
print(f"Personal info: {info}")

print("\n=== Exercise 4: String Methods ===")
# 6. Clean and normalize user input
user_input = "  HELLO World!  "
cleaned = user_input.strip().lower().capitalize()
print(f"Original: '{user_input}'")
print(f"Cleaned: '{cleaned}'")

# 7. Extract domain from email
email = "user@example.com"
username, domain = email.split("@")
print(f"Email: {email}")
print(f"Username: {username}")
print(f"Domain: {domain}")

print("\n=== Exercise 5: Advanced Operations ===")
# 8. Find all vowels in a string
text = "Hello World"
vowels = "aeiouAEIOU"
vowel_count = sum(1 for char in text if char in vowels)
print(f"Text: '{text}'")
print(f"Vowel count: {vowel_count}")

# 9. Convert string to list of characters and back
text = "Python"
char_list = list(text)
print(f"String to list: {char_list}")
back_to_string = "".join(char_list)
print(f"List back to string: {back_to_string}")

# 10. Word frequency counter
sentence = "the quick brown fox jumps over the lazy dog"
words = sentence.split()
word_count = {}
for word in words:
    word_count[word] = word_count.get(word, 0) + 1
print(f"\nWord frequencies: {word_count}")