Python Basics: Getting Started with Python Programming

# In terminal/command prompt
                      python --version
                      # or
                      python3 --version

                      # Expected output: Python 3.x.x

# Numbers - Integers and Floats
age = 25                    # Integer
price = 19.99               # Float
temperature = -5            # Negative integer
pi = 3.14159               # Float

# Strings - Text data
name = "Python"            # Double quotes
greeting = 'Hello, World!' # Single quotes
message = """Multi-line
string example"""          # Triple quotes for multi-line

# String formatting (f-strings - Python 3.6+)
name = "Alice"
age = 30
info = f"My name is {name} and I'm {age} years old"
print(info)  # Output: My name is Alice and I'm 30 years old

# Booleans - True or False
is_active = True
is_complete = False
is_authenticated = True

# Lists - Ordered, mutable collections
fruits = ["apple", "banana", "orange"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]  # Can contain different types

# Accessing list elements
print(fruits[0])      # "apple" (first element)
print(fruits[-1])     # "orange" (last element)
print(fruits[0:2])    # ["apple", "banana"] (slicing)

# Dictionaries - Key-value pairs
person = {
    "name": "John",
    "age": 30,
    "city": "New York",
    "email": "john@example.com"
}

# Accessing dictionary values
print(person["name"])        # "John"
print(person.get("age"))     # 30 (safer method)
print(person.get("phone", "N/A"))  # "N/A" (default if key doesn't exist)

# Tuples - Ordered, immutable collections
coordinates = (10, 20)
colors = ("red", "green", "blue")

# Sets - Unordered, unique elements
unique_numbers = {1, 2, 3, 4, 5}
fruits_set = {"apple", "banana", "orange"}

x = 42
y = "Hello"
z = [1, 2, 3]

print(type(x))  # <class 'int'>
print(type(y))  # <class 'str'>
print(type(z))  # <class 'list'>

# Basic if statement
age = 18
if age >= 18:
    print("You are an adult")
    print("You can vote!")

# If-else statement
temperature = 25
if temperature > 30:
    print("It's hot outside")
else:
    print("It's not too hot")

# If-elif-else (multiple conditions)
score = 85
if score >= 90:
    grade = "A"
    print("Excellent!")
elif score >= 80:
    grade = "B"
    print("Good job!")
elif score >= 70:
    grade = "C"
    print("Not bad")
else:
    grade = "F"
    print("Need improvement")

# Nested if statements
age = 20
has_license = True

if age >= 18:
    if has_license:
        print("You can drive")
    else:
        print("You need a license first")
else:
    print("You're too young to drive")

# Basic for loop with range
for i in range(5):
    print(i)  # Prints 0, 1, 2, 3, 4

# For loop with range(start, stop, step)
for i in range(1, 10, 2):
    print(i)  # Prints 1, 3, 5, 7, 9

# Iterating over a list
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
    print(f"I like {fruit}")

# Iterating with index using enumerate
fruits = ["apple", "banana", "orange"]
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# Iterating over a dictionary
person = {"name": "John", "age": 30, "city": "NYC"}
for key, value in person.items():
    print(f"{key}: {value}")

# Nested loops
for i in range(3):
    for j in range(2):
        print(f"({i}, {j})")  # Prints (0,0), (0,1), (1,0), (1,1), (2,0), (2,1)

# Basic while loop
count = 0
while count < 5:
    print(count)
    count += 1  # Important: increment to avoid infinite loop

# While loop with break
number = 0
while True:
    number += 1
    if number > 10:
        break  # Exit the loop
    print(number)

# While loop with continue
number = 0
while number < 10:
    number += 1
    if number % 2 == 0:
        continue  # Skip even numbers
    print(number)  # Only prints odd numbers: 1, 3, 5, 7, 9

# Practical example: User input validation
while True:
    age = input("Enter your age (or 'quit' to exit): ")
    if age.lower() == 'quit':
        break
    try:
        age_int = int(age)
        if age_int >= 0:
            print(f"Your age is {age_int}")
            break
        else:
            print("Age must be positive")
    except ValueError:
        print("Please enter a valid number")

# Simple function
def greet(name):
    """This function greets a person by name."""
    return f"Hello, {name}!"

# Call the function
message = greet("Python")
print(message)  # Output: Hello, Python!

# Function with multiple parameters
def calculate_area(length, width):
    """Calculate the area of a rectangle."""
    return length * width

area = calculate_area(5, 3)
print(f"Area: {area}")  # Output: Area: 15

# Function with default parameters
def power(base, exponent=2):
    """Calculate base raised to exponent. Default exponent is 2."""
    return base ** exponent

print(power(3))      # 9 (uses default exponent=2)
print(power(3, 3))   # 27 (uses provided exponent=3)

# Function with multiple return values
def get_name_and_age():
    """Return multiple values as a tuple."""
    return "Alice", 30

name, age = get_name_and_age()
print(f"{name} is {age} years old")

# Function with keyword arguments
def create_user(name, age, email, city="Unknown"):
    """Create a user with optional city parameter."""
    return {
        "name": name,
        "age": age,
        "email": email,
        "city": city
    }

# Call with keyword arguments (order doesn't matter)
user1 = create_user(name="John", email="john@example.com", age=25)
user2 = create_user("Jane", 30, "jane@example.com", "NYC")

# Lambda function - simple one-liner functions
square = lambda x: x ** 2
print(square(5))  # 25

# Lambda with multiple parameters
add = lambda x, y: x + y
print(add(3, 4))  # 7

# Using lambda with built-in functions
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x ** 2, numbers))
print(squared)  # [1, 4, 9, 16, 25]

# Filter with lambda
even_numbers = list(filter(lambda x: x % 2 == 0, numbers))
print(even_numbers)  # [2, 4]

# Creating and modifying lists
fruits = ["apple", "banana"]
fruits.append("orange")        # Add to end
fruits.insert(0, "grape")      # Insert at index 0
fruits.remove("banana")        # Remove by value
fruits.pop()                    # Remove and return last item
fruits.pop(0)                   # Remove item at index 0

# List comprehension (Pythonic way)
numbers = [1, 2, 3, 4, 5]
squared = [x ** 2 for x in numbers]  # [1, 4, 9, 16, 25]
evens = [x for x in numbers if x % 2 == 0]  # [2, 4]

# List methods
numbers = [3, 1, 4, 1, 5]
numbers.sort()                  # Sort in place: [1, 1, 3, 4, 5]
numbers.reverse()               # Reverse: [5, 4, 3, 1, 1]
count = numbers.count(1)        # Count occurrences: 2
index = numbers.index(4)        # Find index: 1

# Basic error handling
try:
    number = int(input("Enter a number: "))
    result = 10 / number
    print(f"Result: {result}")
except ValueError:
    print("That's not a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")
except Exception as e:
    print(f"An error occurred: {e}")

# Try-except-else-finally
try:
    file = open("data.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found")
else:
    print("File read successfully")
finally:
    print("This always executes")
    # Close file if it was opened

def calculator():
    """A simple calculator program."""
    print("Welcome to Python Calculator!")
    print("Operations: +, -, *, /")
    
    try:
        num1 = float(input("Enter first number: "))
        operator = input("Enter operator (+, -, *, /): ")
        num2 = float(input("Enter second number: "))
        
        if operator == "+":
            result = num1 + num2
        elif operator == "-":
            result = num1 - num2
        elif operator == "*":
            result = num1 * num2
        elif operator == "/":
            if num2 == 0:
                print("Error: Division by zero!")
                return
            result = num1 / num2
        else:
            print("Invalid operator!")
            return
        
        print(f"{num1} {operator} {num2} = {result}")
    except ValueError:
        print("Error: Please enter valid numbers!")

# Run the calculator
calculator()