Understanding Python: The Versatile Programming Language

Python is a high-level, interpreted programming language known for its simplicity and readability. Created by Guido van Rossum in 1991, Python has become one of the most popular programming languages worldwide due to its versatility and extensive library ecosystem.

What makes Python unique is its clean syntax that emphasizes code readability. It's used in web development, data science, artificial intelligence, machine learning, automation, scientific computing, and much more. Python's "batteries included" philosophy means it comes with a comprehensive standard library.

1. Python Basics & Fundamentals

# Basic variable assignment
name = "Alice"                 # String
age = 25                       # Integer
height = 5.9                   # Float
is_student = True              # Boolean

# Multiple assignment
x, y, z = 1, 2, 3             # x=1, y=2, z=3
a = b = c = 0                  # All variables equal 0

# Type checking and conversion
print(type(age))               # <class 'int'>
print(type(name))              # <class 'str'>
number_str = str(123)          # Convert to string
number_int = int("456")        # Convert to integer

# Arithmetic operators
sum = 10 + 5                   # 15
difference = 10 - 5            # 5
product = 10 * 5               # 50
quotient = 10 / 3              # 3.333... (float division)
floor_division = 10 // 3       # 3 (integer division)
modulus = 10 % 3               # 1
exponent = 2 ** 3              # 8

# Comparison operators
is_equal = 5 == 5              # True
not_equal = 5 != 3             # True
greater_than = 10 > 5          # True
less_than_equal = 5 <= 5       # True

# Logical operators
and_result = True and False    # False
or_result = True or False      # True
not_result = not True          # False

# Basic input and output
name = input("Enter your name: ")
age = input("Enter your age: ")

print("Hello, " + name + "!")
print(f"You are {age} years old.")  # f-string (Python 3.6+)

# Multiple ways to format strings
print("Hello, {}!".format(name))    # .format() method
print("Hello, %s!" % name)          # % formatting

# Printing multiple items
print("Name:", name, "Age:", age)
print("Name: " + name + " Age: " + str(age))

# If-elif-else statements
temperature = 22

if temperature > 30:
    print("It's a hot day!")
    print("Stay hydrated!")
elif temperature > 20:
    print("Perfect weather!")
    print("Enjoy outdoors!")
else:
    print("It's cold outside!")
    print("Dress warmly!")

# Multiple conditions
age = 25
has_license = True

if age >= 18 and has_license:
    print("You can drive!")
else:
    print("You cannot drive.")

# Ternary operator
status = "adult" if age >= 18 else "minor"
print(f"Status: {status}")

# For loop with range
for i in range(5):             # 0 to 4
    print(f"Iteration {i}")

for i in range(1, 6):          # 1 to 5
    print(f"Count: {i}")

for i in range(0, 10, 2):      # 0, 2, 4, 6, 8
    print(f"Even: {i}")

# While loop
count = 0
while count < 5:
    print(f"While count: {count}")
    count += 1

# Loop control statements
for i in range(10):
    if i == 3:
        continue               # Skip iteration
    if i == 7:
        break                  # Exit loop
    print(i)

2. Data Structures

# Creating lists
fruits = ["apple", "banana", "orange"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]

# Accessing elements
print(fruits[0])               # "apple" (first element)
print(fruits[-1])              # "orange" (last element)

# Slicing lists
print(numbers[1:3])            # [2, 3] (elements 1 to 2)
print(numbers[:3])             # [1, 2, 3] (first three)
print(numbers[2:])             # [3, 4, 5] (from index 2)

# List methods
fruits.append("grape")         # Add to end
fruits.insert(1, "mango")      # Insert at position
fruits.remove("banana")        # Remove element
popped = fruits.pop()          # Remove and return last element
fruits.sort()                  # Sort in place
fruits.reverse()               # Reverse in place

# List comprehension (powerful feature!)
squares = [x**2 for x in range(1, 6)]  # [1, 4, 9, 16, 25]
even_squares = [x**2 for x in range(1, 11) if x % 2 == 0]

# Creating tuples
coordinates = (10, 20)
person = ("Alice", 25, "Engineer")
single_element = (42,)         # Note the comma for single element

# Accessing tuple elements
print(coordinates[0])          # 10
print(person[1])               # 25

# Tuple unpacking
x, y = coordinates             # x=10, y=20
name, age, job = person        # name="Alice", age=25, job="Engineer"

# Tuples are immutable
# coordinates[0] = 15         # This would cause an error!

# Converting between list and tuple
numbers_list = [1, 2, 3]
numbers_tuple = tuple(numbers_list)
tuple_to_list = list(numbers_tuple)

# Creating dictionaries
student = {
    "name": "Alice",
    "age": 20,
    "major": "Computer Science",
    "grades": [85, 92, 78]
}

# Accessing values
print(student["name"])          # "Alice"
print(student.get("age"))       # 20
print(student.get("phone", "Not provided"))  # Default value

# Adding and modifying
student["email"] = "alice@school.edu"  # Add new key
student["age"] = 21             # Modify existing key

# Dictionary methods
keys = student.keys()           # Get all keys
values = student.values()       # Get all values
items = student.items()         # Get key-value pairs

# Dictionary comprehension
squares_dict = {x: x**2 for x in range(1, 6)}  # {1:1, 2:4, 3:9, 4:16, 5:25}

# Iterating through dictionary
for key, value in student.items():
    print(f"{key}: {value}")

# Creating sets
fruits = {"apple", "banana", "orange"}
numbers = {1, 2, 3, 4, 5}
empty_set = set()               # Note: {} creates empty dict!

# Sets automatically remove duplicates
colors = {"red", "blue", "green", "red", "blue"}
print(colors)                   # {"red", "blue", "green"}

# Set operations
set1 = {1, 2, 3, 4, 5}
set2 = {4, 5, 6, 7, 8}

union = set1 | set2             # {1, 2, 3, 4, 5, 6, 7, 8}
intersection = set1 & set2      # {4, 5}
difference = set1 - set2        # {1, 2, 3}
symmetric_diff = set1 ^ set2    # {1, 2, 3, 6, 7, 8}

# Set methods
fruits.add("mango")             # Add element
fruits.remove("apple")          # Remove element (error if not exists)
fruits.discard("banana")        # Remove element (no error)
fruits.pop()                    # Remove random element

3. Functions & Modules

# Basic function definition
def greet(name):
    """This function greets the person passed as parameter"""
    return f"Hello, {name}!"

# Function call
message = greet("Alice")
print(message)                  # "Hello, Alice!"

# Function with multiple parameters
def calculate_area(length, width):
    area = length * width
    return area

room_area = calculate_area(10, 5)
print(f"Room area: {room_area} square units")

# Function with default parameters
def create_user(name, age=18, is_active=True):
    """Create user with optional parameters"""
    return {
        "username": name,
        "user_age": age,
        "active": is_active
    }

user1 = create_user("Bob")      # Uses default age and status
user2 = create_user("Charlie", 25, False)

# *args for variable positional arguments
def sum_all(*numbers):
    """Sum all provided numbers"""
    total = 0
    for num in numbers:
        total += num
    return total

result1 = sum_all(1, 2, 3)     # 6
result2 = sum_all(1, 2, 3, 4, 5) # 15

# **kwargs for variable keyword arguments
def create_profile(**details):
    """Create user profile from keyword arguments"""
    profile = {}
    for key, value in details.items():
        profile[key] = value
    return profile

user_profile = create_profile(
    name="Alice",
    age=25,
    city="New York",
    job="Developer"
)

# Lambda functions (anonymous functions)
square = lambda x: x ** 2
print(square(5))               # 25

# Using lambda with map and filter
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, numbers))  # [1, 4, 9, 16, 25]
evens = list(filter(lambda x: x % 2 == 0, numbers))  # [2, 4]

# Importing entire module
import math
import random

print(math.sqrt(16))           # 4.0
print(random.randint(1, 10))   # Random number between 1-10

# Import specific functions
from datetime import datetime, date
from math import pi, sin, cos

print(pi)                      # 3.141592653589793
current_time = datetime.now()
print(f"Current time: {current_time}")

# Import with alias
import numpy as np
import pandas as pd

# Creating and using your own module
# File: utils.py
def calculate_tax(amount, tax_rate=0.15):
    return amount * tax_rate

def format_currency(amount):
    return f"${amount:.2f}"

# In main file:
# from utils import calculate_tax, format_currency
# tax = calculate_tax(100)
# print(format_currency(tax))