Basics

python --version  # On Windows
python3 --version  # On macOS/Linux

# This is a comment - Python ignores this line
print("Hello, World!")  # This prints text to the console

# Save this code in a file named hello.py
# Run it by typing 'python hello.py' in your terminal

# Variable assignment
name = "John"     # String - text
age = 30          # Integer - whole number
height = 5.11     # Float - decimal number
is_student = True # Boolean - True/False

# Python is dynamically typed - no need to declare variable types
# Variable names are case-sensitive: 'name' and 'Name' are different

# Basic operations
sum_result = 5 + 10       # Addition: 15
difference = 10 - 5       # Subtraction: 5
product = 4 * 5           # Multiplication: 20
quotient = 20 / 4         # Division: 5.0 (always returns float)
integer_division = 20 // 4 # Floor division: 5 (returns int)
remainder = 10 % 3        # Modulo (remainder): 1
power = 2 ** 3            # Exponentiation: 8 (2 raised to power 3)

# Type conversion
int_from_str = int("42")     # Convert string to int: 42
float_from_str = float("3.14") # Convert string to float: 3.14
str_from_num = str(42)       # Convert number to string: "42"

# Check type of a variable
print(type(sum_result))      # <class 'int'>

# String creation
single_quotes = 'Hello'
double_quotes = "World"
triple_quotes = '''Multiple
lines of text'''

# String operations
greeting = single_quotes + " " + double_quotes  # Concatenation: "Hello World"
repeated = "Ha" * 3  # Repetition: "HaHaHa"

# String methods
name = "Python"
print(name.upper())          # "PYTHON" - all uppercase
print(name.lower())          # "python" - all lowercase
print(len(name))             # 6 - length of string
print(name.replace('P', 'J')) # "Jython" - replace characters
print("th" in name)          # True - check if substring exists

# String formatting (f-strings - Python 3.6+)
name = "Alice"
age = 25
intro = f"My name is {name} and I'm {age} years old."
# Output: "My name is Alice and I'm 25 years old."

# Creating lists
fruits = ["apple", "banana", "cherry"]  # List of strings
mixed = [1, "hello", 3.14, True]        # List with different data types

# Accessing elements (zero-indexed)
first_fruit = fruits[0]   # "apple" - first item
last_fruit = fruits[-1]   # "cherry" - last item

# Slicing lists
subset = fruits[0:2]      # ["apple", "banana"] - items from index 0 up to (not including) 2

# Modifying lists
fruits.append("orange")   # Add item to end: ["apple", "banana", "cherry", "orange"]
fruits.insert(1, "mango") # Insert at position: ["apple", "mango", "banana", "cherry", "orange"]
fruits.remove("banana")   # Remove by value: ["apple", "mango", "cherry", "orange"]
popped = fruits.pop()     # Remove and return last item: "orange"
fruits[0] = "pear"        # Change item at index: ["pear", "mango", "cherry"]

# List operations
nums = [3, 1, 4, 1, 5, 9]
nums.sort()               # Sort in-place: [1, 1, 3, 4, 5, 9]
nums.reverse()            # Reverse in-place: [9, 5, 4, 3, 1, 1]
print(len(nums))          # Length: 6
print(sum(nums))          # Sum: 23
print(max(nums))          # Maximum: 9
print(min(nums))          # Minimum: 1

# Creating tuples
coordinates = (10.5, 20.8)
single_item = (42,)  # Comma is needed for single-item tuples

# Accessing elements (same as lists)
x_coord = coordinates[0]  # 10.5

# Cannot modify tuples!
# coordinates[0] = 15  # This would cause an error

# Tuple unpacking
x, y = coordinates  # x = 10.5, y = 20.8

# Creating dictionaries
person = {
    "name": "John",
    "age": 30,
    "is_student": False
}

# Accessing values
name = person["name"]     # "John"
# Safer access with get (returns None or default if key doesn't exist)
height = person.get("height")         # None
height = person.get("height", 175)    # 175 (default value)

# Modifying dictionaries
person["age"] = 31        # Change value
person["height"] = 180    # Add new key-value pair
del person["is_student"]  # Remove key-value pair

# Dictionary methods
keys = list(person.keys())      # Get all keys: ['name', 'age', 'height']
values = list(person.values())  # Get all values: ['John', 31, 180]

# Checking if a key exists
if "name" in person:
    print("Name exists!")

# Creating sets
fruits = {"apple", "banana", "cherry"}
numbers = set([1, 2, 2, 3, 3, 4])  # Creates {1, 2, 3, 4} - duplicates removed

# Adding/removing items
fruits.add("orange")      # Add item
fruits.remove("banana")   # Remove item (raises error if not found)
fruits.discard("mango")   # Remove item (no error if not found)

# Set operations
set1 = {1, 2, 3}
set2 = {3, 4, 5}
union = set1 | set2       # Union: {1, 2, 3, 4, 5}
intersection = set1 & set2 # Intersection: {3}
difference = set1 - set2  # Difference: {1, 2}

# if-elif-else statement
age = 20

if age < 18:
    print("You are a minor")
elif age >= 18 and age < 65:
    print("You are an adult")
else:
    print("You are a senior")
# Output: "You are an adult"

# Comparison operators
x, y = 5, 10
print(x == y)  # Equal to: False
print(x != y)  # Not equal to: True
print(x < y)   # Less than: True
print(x > y)   # Greater than: False

# Logical operators
a, b = True, False
print(a and b)  # Logical AND: False
print(a or b)   # Logical OR: True
print(not a)    # Logical NOT: False

# Iterating through a sequence
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)
# Output: apple, banana, cherry (each on a new line)

# Using range
for i in range(5):  # 0 to 4
    print(i, end=" ")
# Output: 0 1 2 3 4

# Enumerate for index and value
for index, value in enumerate(fruits):
    print(f"Index {index}: {value}")
# Output: Index 0: apple, Index 1: banana, Index 2: cherry

# Basic while loop
count = 0
while count < 5:
    print(count, end=" ")
    count += 1  # Don't forget to update the condition!
# Output: 0 1 2 3 4

# Break and continue
i = 1
while i <= 10:
    if i % 2 == 0:
        i += 1
        continue  # Skip even numbers
    if i > 7:
        break     # Exit loop when i > 7
    print(i, end=" ")
    i += 1
# Output: 1 3 5 7

# Basic function
def greet():
    """This docstring describes what the function does"""
    print("Hello, world!")

# Function with parameters
def greet_person(name):
    print(f"Hello, {name}!")

# Function with default parameter
def greet_with_time(name, time="morning"):
    print(f"Good {time}, {name}!")

# Function with return value
def add(a, b):
    return a + b

# Call the functions
greet()                          # Hello, world!
greet_person("Alice")            # Hello, Alice!
greet_with_time("Bob")           # Good morning, Bob!
greet_with_time("Charlie", "evening") # Good evening, Charlie!
result = add(5, 3)               # result = 8

# *args for variable positional arguments
def add_all(*numbers):
    """Accepts any number of arguments and returns their sum"""
    return sum(numbers)

print(add_all(1, 2, 3, 4))  # 10
print(add_all(5, 10))       # 15

# **kwargs for variable keyword arguments
def build_profile(**user_info):
    """Creates a dictionary with all keyword arguments"""
    return user_info

profile = build_profile(name="John", age=30, job="Developer")
# Returns {'name': 'John', 'age': 30, 'job': 'Developer'}

# Importing an entire module
import math
print(math.sqrt(16))  # 4.0

# Importing specific items
from math import pi, cos
print(pi)       # 3.141592653589793
print(cos(0))   # 1.0

# Importing with an alias
import math as m
print(m.sqrt(25))  # 5.0

# Writing to a file
with open("example.txt", "w") as file:
    file.write("Hello, world!\n")
    file.write("This is a text file.\n")
    # File is automatically closed when the block ends

# Reading a file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)
    # Output: Hello, world!
    #         This is a text file.

# Reading line by line
with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())  # strip() removes the newline character

import json

# Converting Python object to JSON string
data = {
    "name": "John",
    "age": 30,
    "city": "New York"
}
json_string = json.dumps(data, indent=4)
print(json_string)
# Output:
# {
#     "name": "John",
#     "age": 30,
#     "city": "New York"
# }

# Writing JSON to a file
with open("data.json", "w") as file:
    json.dump(data, file, indent=4)

# Reading JSON from a file
with open("data.json", "r") as file:
    loaded_data = json.load(file)
    print(loaded_data["name"])  # "John"

# Basic try-except
try:
    result = 10 / 0  # This will cause a ZeroDivisionError
except ZeroDivisionError:
    print("Cannot divide by zero!")

# Handling multiple exceptions
try:
    number = int(input("Enter a number: "))  # Could cause ValueError
    result = 10 / number  # Could cause ZeroDivisionError
except ValueError:
    print("That's not a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")

# Try-except-else-finally
try:
    file = open("example.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found!")
else:
    # This runs if no exception occurs
    print(f"File content: {content}")
finally:
    # This runs no matter what
    if 'file' in locals():  # Check if file was opened successfully
        file.close()
    print("Operation attempted")

# Creating a simple class
class Dog:
    # Class attribute (shared by all instances)
    species = "Canis familiaris"

    # Initializer / Constructor
    def __init__(self, name, age):
        # Instance attributes (unique to each instance)
        self.name = name
        self.age = age

    # Instance method
    def description(self):
        return f"{self.name} is {self.age} years old"

    # Another instance method
    def speak(self, sound):
        return f"{self.name} says {sound}"

# Creating instances of the class
buddy = Dog("Buddy", 9)
miles = Dog("Miles", 4)

# Accessing attributes
print(buddy.name)      # "Buddy"
print(buddy.species)   # "Canis familiaris" (class attribute)

# Calling methods
print(buddy.description())     # "Buddy is 9 years old"
print(miles.speak("Woof!"))    # "Miles says Woof!"

# Parent class
class Pet:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def show(self):
        print(f"I am {self.name} and I am {self.age} years old")

    def speak(self):
        print("I don't know what to say")

# Child class inheriting from Pet
class Cat(Pet):
    def __init__(self, name, age, color):
        super().__init__(name, age)  # Call the parent initializer
        self.color = color

    # Override the parent's speak method
    def speak(self):
        print("Meow")

    # Override the parent's show method
    def show(self):
        print(f"I am {self.name}, a {self.color} cat, and I am {self.age} years old")

# Create a Cat object
felix = Cat("Felix", 3, "black")
felix.show()  # "I am Felix, a black cat, and I am 3 years old"
felix.speak()  # "Meow"

# Install a package
pip install requests

# Install a specific version
pip install requests==2.28.1

# Upgrade a package
pip install --upgrade requests

# List installed packages
pip list

# Uninstall a package
pip uninstall requests

# Create a virtual environment
python -m venv myenv  # Windows
python3 -m venv myenv  # macOS/Linux

# Activate the environment
myenv\Scripts\activate  # Windows
source myenv/bin/activate  # macOS/Linux

# Deactivate the environment
deactivate

import json
import os

# File to store the tasks
TASKS_FILE = "tasks.json"

def load_tasks():
    """Load tasks from file or return empty list if file doesn't exist"""
    if os.path.exists(TASKS_FILE):
        with open(TASKS_FILE, 'r') as file:
            try:
                return json.load(file)
            except json.JSONDecodeError:
                return []  # Return empty list if file is corrupted
    return []  # Return empty list if file doesn't exist

def save_tasks(tasks):
    """Save tasks to file"""
    with open(TASKS_FILE, 'w') as file:
        json.dump(tasks, file, indent=4)  # Save with nice formatting

def show_tasks(tasks):
    """Display all tasks with their indices"""
    if not tasks:
        print("No tasks yet!")
        return

    print("\n=== YOUR TASKS ===")
    for i, task in enumerate(tasks, 1):  # Start counting from 1
        status = "✓" if task["completed"] else " "
        print(f"{i}. [{status}] {task['title']}")
    print()

def add_task(tasks, title):
    """Add a new task"""
    tasks.append({"title": title, "completed": False})
    save_tasks(tasks)
    print(f"Task '{title}' added successfully!")

def complete_task(tasks, index):
    """Mark a task as completed"""
    if 1 <= index <= len(tasks):  # Check if index is valid
        tasks[index-1]["completed"] = True
        save_tasks(tasks)
        print(f"Task '{tasks[index-1]['title']}' marked as completed!")
    else:
        print("Invalid task number!")

def delete_task(tasks, index):
    """Delete a task"""
    if 1 <= index <= len(tasks):  # Check if index is valid
        deleted = tasks.pop(index-1)
        save_tasks(tasks)
        print(f"Task '{deleted['title']}' deleted!")
    else:
        print("Invalid task number!")

def main():
    """Main function to run the to-do list application"""
    tasks = load_tasks()

    while True:
        print("\n==== TO-DO LIST APP ====")
        print("1. Show tasks")
        print("2. Add task")
        print("3. Mark task as completed")
        print("4. Delete task")
        print("5. Exit")

        choice = input("\nEnter your choice (1-5): ")

        if choice == '1':
            show_tasks(tasks)

        elif choice == '2':
            title = input("Enter task title: ")
            add_task(tasks, title)

        elif choice == '3':
            show_tasks(tasks)
            try:
                index = int(input("Enter task number to mark as completed: "))
                complete_task(tasks, index)
            except ValueError:
                print("Please enter a valid number!")

        elif choice == '4':
            show_tasks(tasks)
            try:
                index = int(input("Enter task number to delete: "))
                delete_task(tasks, index)
            except ValueError:
                print("Please enter a valid number!")

        elif choice == '5':
            print("Goodbye!")
            break

        else:
            print("Invalid choice. Please try again.")

if __name__ == "__main__":
    main()

# To run this app:
# 1. Save this code to a file named todo.py
# 2. Open your terminal/command prompt
# 3. Navigate to the directory containing todo.py
# 4. Run the command: python todo.py