15_strings.py

# strings in Python are immutable

s = "Hello"
s[0] = "h"  # ❌ This will raise an error

# --------
s = "  Hello, Python!  "

# 1. Case Conversion
print(s.upper())   # "  HELLO, PYTHON!  "
print(s.lower())   # "  hello, python!  "
print(s.strip())   # "Hello, Python!" (removes spaces)

# 2. Search and Replace
print(s.find("Python"))   # 9 (index of first occurrence)
print(s.replace("Python", "World"))  # "  Hello, World!  "

# 3. String Checking
print("hello".isalpha())  # True (all letters)
print("123".isdigit())    # True (all digits)
print("hello123".isalnum())  # True (letters + digits)

# 4. Splitting and Joining
words = s.split(",")  # Splits at comma
print(words)  # ['  Hello', ' Python!  ']
print("-".join(words))  # "  Hello- Python!  "