Lecture 4: Strings and Data Types

Immutable Example (String):

# Strings are immutable
text = "Hello"
print(f"Original: {text}")
print(f"ID: {id(text)}")

# This creates a new string, doesn't modify the original
text = text + " World"
print(f"Modified: {text}")
print(f"New ID: {id(text)}")  # Different ID

Mutable Example (List):

# Lists are mutable
numbers = [1, 2, 3]
print(f"Original: {numbers}")
print(f"ID: {id(numbers)}")

# This modifies the original list
numbers.append(4)
print(f"Modified: {numbers}")
print(f"Same ID: {id(numbers)}")  # Same ID

# Single quotes
name = 'John Doe'

# Double quotes
message = "Hello, World!"

# Triple quotes (for multiline strings)
paragraph = """This is a
multiline string that can span
multiple lines."""

# Raw strings (no escape sequences)
path = r"C:\Users\Documents\file.txt"

text = "Python Programming"

# Indexing (0-based)
print(text[0])     # Output: P
print(text[-1])    # Output: g (last character)

# Slicing [start:end:step]
print(text[0:6])           # Output: Python
print(text[7:])            # Output: Programming
print(text[::2])           # Output: Pto rgamn
print(text[::-1])          # Output: gnimmargorP nohtyP (reversed)

text = "Hello, World!"
print(len(text))  # Output: 13

text = "  Python Programming is Fun!  "

# Case conversion methods
print(text.upper())        # "  PYTHON PROGRAMMING IS FUN!  "
print(text.lower())        # "  python programming is fun!  "
print(text.title())        # "  Python Programming Is Fun!  "
print(text.capitalize())   # "  python programming is fun!  "

# Whitespace methods
print(text.strip())        # "Python Programming is Fun!"
print(text.lstrip())       # "Python Programming is Fun!  "
print(text.rstrip())       # "  Python Programming is Fun!"

# Search methods
print(text.find("Python")) # 2
print(text.count("i"))      # 2
print(text.startswith("  ")) # True
print(text.endswith("!  "))  # True

# Replacement
print(text.replace("Fun", "Awesome")) # "  Python Programming is Awesome!  "

# Splitting and joining
words = text.strip().split()
print(words)  # ["Python", "Programming", "is", "Fun!"]
joined = "-".join(words)
print(joined)  # "Python-Programming-is-Fun!"

# Addition operator (+) for concatenation
first_name = "John"
last_name = "Doe"
full_name = first_name + " " + last_name
print(full_name)  # Output: John Doe

# Multiple concatenation
greeting = "Hello" + ", " + "World" + "!"
print(greeting)  # Output: Hello, World!

# Multiplication operator (*) for repetition
pattern = "*" * 10
print(pattern)  # Output: **********

word = "Python "
repeated = word * 3
print(repeated)  # Output: Python Python Python 

text = "Python Programming"

# in operator
print("Python" in text)      # True
print("Java" in text)        # False

# not in operator
print("Java" not in text)    # True

# Lexicographical comparison
str1 = "apple"
str2 = "banana"

print(str1 < str2)   # True (a comes before b)
print(str1 > str2)   # False
print(str1 == str2)  # False
print(str1 != str2)  # True

# Case-sensitive comparison
print("Apple" < "apple")  # True (uppercase comes before lowercase)

# Old style formatting (% operator)
name = "John"
age = 25
print("Name: %s, Age: %d" % (name, age))

# f-strings (recommended)
print(f"Name: {name}, Age: {age}")

# format() method
print("Name: {}, Age: {}".format(name, age))

text = "Python Programming"

# Basic slicing
print(text[0:6])     # Python
print(text[7:])      # Programming
print(text[:6])      # Python

# Step slicing
print(text[::2])     # Pto rgamn
print(text[::-1])    # gnimmargorP nohtyP (reversed)

# Quotes in strings
message1 = "He said, \"Hello, World!\""
message2 = 'It\'s a beautiful day'

# Newlines and tabs
address = "John Doe\n123 Main St\tNew York, NY"
print(address)

# Backslashes
file_path = "C:\\Users\\Documents\\file.txt"
print(file_path)

# Unicode characters
greek_letter = "\u03A9"  # Omega symbol
emoji = "\U0001F600"     # Smiling face emoji
print(f"Greek: {greek_letter}, Emoji: {emoji}")

# Raw strings (no escape sequences)
raw_path = r"C:\Users\Documents\file.txt"
print(raw_path)