Unit I: Introduction to Python

# This is your first Python program
print("Hello, World!")

# You can also print numbers
print(42)

# And perform calculations
print(10 + 20)

# Creating variables
name = "John"           # String variable
age = 25                # Integer variable
height = 5.9            # Float variable
is_student = True       # Boolean variable

# Printing variables
print("Name:", name)
print("Age:", age)
print("Height:", height)
print("Is Student:", is_student)

# Valid variable names
my_name = "Alice"
myName = "Bob"           # camelCase
MyName = "Charlie"       # PascalCase
_private = "hidden"
name2 = "David"
CONSTANT_VALUE = 100

# Invalid variable names (will cause errors)
# 2name = "Error"        # Cannot start with number
# my-name = "Error"      # Cannot use hyphen
# my name = "Error"      # Cannot have spaces

# Assign same value to multiple variables
x = y = z = 50
print(x, y, z)  # Output: 50 50 50

# Assign different values to multiple variables
a, b, c = 10, 20, 30
print(a, b, c)  # Output: 10 20 30

# Swap variables
x = 5
y = 10
x, y = y, x
print("x =", x, "y =", y)  # Output: x = 10 y = 5

# Arithmetic operators examples
a = 10
b = 3

print("Addition:", a + b)        # 13
print("Subtraction:", a - b)     # 7
print("Multiplication:", a * b)  # 30
print("Division:", a / b)        # 3.333...
print("Floor Division:", a // b) # 3
print("Modulus:", a % b)         # 1
print("Power:", a ** b)          # 1000

# Assignment operators
x = 10      # Assign
x += 5      # Add and assign (x = x + 5), x = 15
x -= 3      # Subtract and assign (x = x - 3), x = 12
x *= 2      # Multiply and assign (x = x * 2), x = 24
x /= 4      # Divide and assign (x = x / 4), x = 6.0
x //= 2     # Floor divide and assign, x = 3.0
x %= 2      # Modulus and assign, x = 1.0
x **= 3     # Power and assign, x = 1.0

print("Final value:", x)

# Logical operators
a = True
b = False

print("a and b:", a and b)  # False (both must be True)
print("a or b:", a or b)    # True (at least one must be True)
print("not a:", not a)      # False (reverses the value)

# Practical example
age = 25
has_license = True

can_drive = age >= 18 and has_license
print("Can drive:", can_drive)  # True

# Identity operators (is, is not)
x = [1, 2, 3]
y = [1, 2, 3]
z = x

print(x is z)       # True (same object)
print(x is y)       # False (different objects)
print(x == y)       # True (same values)
print(x is not y)   # True

# Membership operators (in, not in)
fruits = ["apple", "banana", "cherry"]
print("banana" in fruits)      # True
print("grape" not in fruits)   # True

# Also works with strings
name = "Python"
print("y" in name)   # True

# Python blocks example
age = 20

# Block starts after colon (:)
if age >= 18:
    # This is inside the if block (4 spaces indentation)
    print("You are an adult")
    print("You can vote")
    
    if age >= 21:
        # Nested block (8 spaces indentation)
        print("You can also drink in the US")
        
# This is outside the if block (no indentation)
print("Age verification complete")

# Function block example
def greet(name):
    # Function body block
    message = f"Hello, {name}!"
    print(message)
    return message

greet("Alice")

# WRONG - This will cause an error!
# if True:
#     print("Hello")
#   print("World")  # IndentationError: unexpected indent

# CORRECT
if True:
    print("Hello")
    print("World")  # Same indentation

# Different data types in Python

# String
name = "Python"
print(type(name))  # <class 'str'>

# Integer
age = 30
print(type(age))   # <class 'int'>

# Float
price = 19.99
print(type(price)) # <class 'float'>

# Boolean
is_active = True
print(type(is_active))  # <class 'bool'>

# List
fruits = ["apple", "banana", "cherry"]
print(type(fruits))  # <class 'list'>

# Tuple
coordinates = (10, 20)
print(type(coordinates))  # <class 'tuple'>

# Dictionary
person = {"name": "John", "age": 30}
print(type(person))  # <class 'dict'>

# Set
unique_numbers = {1, 2, 3, 4, 5}
print(type(unique_numbers))  # <class 'set'>

# None
result = None
print(type(result))  # <class 'NoneType'>

# Type conversion (Casting)

# String to Integer
num_str = "100"
num_int = int(num_str)
print(num_int + 50)  # 150

# Integer to String
age = 25
age_str = str(age)
print("I am " + age_str + " years old")

# Float to Integer (truncates decimal)
price = 19.99
price_int = int(price)
print(price_int)  # 19

# Integer to Float
count = 10
count_float = float(count)
print(count_float)  # 10.0

# String to List
name = "Python"
letters = list(name)
print(letters)  # ['P', 'y', 't', 'h', 'o', 'n']

# List to Tuple
my_list = [1, 2, 3]
my_tuple = tuple(my_list)
print(my_tuple)  # (1, 2, 3)

# Integer examples
positive = 42
negative = -17
zero = 0
large_number = 123456789012345678901234567890  # No limit!

print(type(positive))  # <class 'int'>

# Different number systems
binary = 0b1010       # Binary (base 2) = 10
octal = 0o17          # Octal (base 8) = 15
hexadecimal = 0xFF    # Hexadecimal (base 16) = 255

print(f"Binary 0b1010 = {binary}")
print(f"Octal 0o17 = {octal}")
print(f"Hex 0xFF = {hexadecimal}")

# Underscore for readability (Python 3.6+)
billion = 1_000_000_000
print(billion)  # 1000000000

# Float examples
pi = 3.14159
temperature = -40.5
small = 0.0001

print(type(pi))  # <class 'float'>

# Scientific notation
speed_of_light = 3e8       # 3 × 10^8 = 300000000.0
tiny = 1.5e-10             # 1.5 × 10^-10

print(f"Speed of light: {speed_of_light}")
print(f"Tiny number: {tiny}")

# Float precision warning
result = 0.1 + 0.2
print(result)  # 0.30000000000000004 (floating point precision)

# For precise calculations, use decimal module
from decimal import Decimal
precise = Decimal('0.1') + Decimal('0.2')
print(precise)  # 0.3

# Complex number examples
z1 = 3 + 4j
z2 = complex(2, 5)  # 2 + 5j

print(type(z1))     # <class 'complex'>
print(z1.real)      # 3.0 (real part)
print(z1.imag)      # 4.0 (imaginary part)

# Complex arithmetic
z3 = z1 + z2
print(f"Sum: {z3}")  # (5+9j)

z4 = z1 * z2
print(f"Product: {z4}")  # (-14+23j)

# Absolute value (magnitude)
print(abs(z1))  # 5.0 (√(3² + 4²))

# Built-in numeric functions
import math

# Basic functions
print(abs(-10))        # 10 (absolute value)
print(round(3.7))      # 4 (round to nearest)
print(round(3.14159, 2))  # 3.14 (round to 2 decimals)
print(pow(2, 3))       # 8 (power)
print(max(1, 5, 3))    # 5 (maximum)
print(min(1, 5, 3))    # 1 (minimum)
print(sum([1, 2, 3]))  # 6 (sum of iterable)

# Math module functions
print(math.sqrt(16))   # 4.0 (square root)
print(math.ceil(3.2))  # 4 (ceiling)
print(math.floor(3.8)) # 3 (floor)
print(math.pi)         # 3.141592653589793
print(math.e)          # 2.718281828459045
print(math.sin(0))     # 0.0
print(math.log(10))    # 2.302... (natural log)
print(math.log10(100)) # 2.0