Python 3 — String Slicing & Methods

# Single and double quotes
name1 = 'Python'
name2 = "Python"
print(name1 == name2)   # True — same thing

# Triple quotes for multi-line strings
poem = """Roses are red,
Violets are blue,
Python is awesome,
And so are you!"""
print(poem)

# Escape characters
path = "C:\Users\Balaji\Documents"
tab_example = "Name:\tBalaji"
newline = "Line 1\nLine 2"
print(path)
print(tab_example)
print(newline)

# Raw strings (r-prefix) — backslashes are literal
raw = r"C:UsersBalajiDocuments"
print(raw)

text = "Hello, Python!"
#       0123456789...

# Single character access
print(text[0])     # H
print(text[7])     # P
print(text[-1])    # !
print(text[-6])    # P

# Slicing: [start:stop:step]
print(text[0:5])   # Hello
print(text[7:13])  # Python
print(text[:5])    # Hello (start defaults to 0)
print(text[7:])    # Python! (stop defaults to end)
print(text[::2])   # Hlo yhn (every 2nd char)
print(text[::-1])  # !nohtyP ,olleH (reversed!)

name = "Balaji"
score = 98.567
items = 5

# F-string with expressions
print(f"Hello, {name}!")
print(f"Score: {score:.2f}")    # 2 decimal places
print(f"Items: {items:03d}")    # pad with zeros: 005
print(f"Name upper: {name.upper()}")
print(f"2^10 = {2**10}")

# Width and alignment
print(f"{'Left':<10}|")        # Left-aligned
print(f"{'Right':>10}|")       # Right-aligned
print(f"{'Center':^10}|")      # Centered

# Old-style formatting (still common)
msg = "Hello %s, you are %d years old." % ("Bob", 30)
print(msg)

# .format() method
msg2 = 'Product: {}, Price: $' + '{:.2f}'.format("Laptop", 999.99)
print(msg2)

text = "  Hello, World! Python is Amazing.  "

# Cleaning
clean = text.strip()
print(clean)                        # No leading/trailing spaces

# Case methods
print(clean.upper())                # ALL CAPS
print(clean.lower())                # all lowercase
print(clean.title())                # Title Case
print(clean.swapcase())             # sWAP cASE

# Finding & replacing
print(clean.find("Python"))         # 15 (index)
print(clean.count("o"))             # 4
print(clean.replace("Amazing", "Awesome"))

# Splitting & joining
sentence = "apple,banana,cherry,mango"
fruits = sentence.split(",")
print(fruits)                       # ['apple', 'banana', ...]
rejoined = " | ".join(fruits)
print(rejoined)                     # apple | banana | ...

# Check string contents
print("Python3".isalpha())   # False (has digit)
print("Python".isalpha())    # True (only letters)
print("12345".isdigit())     # True (only digits)
print("Hello123".isalnum())  # True (letters + digits)
print("   ".isspace())       # True (only whitespace)
print("hello".islower())     # True
print("HELLO".isupper())     # True
print("Hello World".istitle()) # True

# Common validation patterns
email = "user@example.com"
print("@" in email and "." in email)  # True

phone = "9876543210"
print(phone.isdigit() and len(phone) == 10)  # True

# Concatenation with +
first = "Hello"
second = "World"
greeting = first + ", " + second + "!"
print(greeting)   # Hello, World!

# Repetition with *
divider = "-" * 40
print(divider)

stars = "⭐" * 5
print(stars)   # ⭐⭐⭐⭐⭐

# Building strings with join (efficient for many strings)
words = ["Python", "is", "a", "great", "language"]
sentence = " ".join(words)
print(sentence)

# Strings are immutable — can't modify in place
name = "Python"
# name[0] = "J"  # ❌ TypeError!
name = "J" + name[1:]  # ✅ Create new string
print(name)

# Palindrome check
def is_palindrome(s):
    s = s.lower().replace(" ", "")
    return s == s[::-1]

print(is_palindrome("racecar"))    # True
print(is_palindrome("A man a plan a canal Panama"))  # True
print(is_palindrome("Python"))     # False

# Word count
text = "the quick brown fox jumps over the lazy dog"
words = text.split()
word_count = {}
for word in words:
    word_count[word] = word_count.get(word, 0) + 1
print(word_count)

# Extract file extension
filename = "tutorial.python.pdf"
parts = filename.rsplit(".", 1)
print(f"Name: {parts[0]}, Extension: {parts[1]}")