Learn PYTHON with Real Code Examples

import math
from typing import List, Optional

def fibonacci(n: int) -> List[int]:
    """Generate fibonacci sequence up to n numbers"""
    if n <= 0:
        return []
    elif n == 1:
        return [0]

    fib = [0, 1]
    for i in range(2, n):
        fib.append(fib[i-1] + fib[i-2])
    return fib

def find_primes(limit: int) -> List[int]:
    """Find all prime numbers up to limit using sieve"""
    primes = []
    sieve = [True] * (limit + 1)

    for i in range(2, int(math.sqrt(limit)) + 1):
        if sieve[i]:
        for j in range(i * i, limit + 1, i):
        sieve[j] = False

    return [i for i in range(2, limit + 1) if sieve[i]]

# Main execution
if __name__ == "__main__":
    fib_sequence = fibonacci(10)
    print(f"Fibonacci: {fib_sequence}")

    primes = find_primes(30)
    print(f"Primes up to 30: {primes}")

    # List comprehension example
    squares = [x**2 for x in range(1, 11) if x % 2 == 0]
    print(f"Even squares: {squares}")

Demonstrates Python's list comprehension, type hints, and function definitions with docstrings.

def quick_sort(arr):
    if len(arr) <= 1:
        return arr
    pivot = arr[len(arr) // 2]
    left = [x for x in arr if x < pivot]
    middle = [x for x in arr if x == pivot]
    right = [x for x in arr if x > pivot]
    return quick_sort(left) + middle + quick_sort(right)

# Example usage
if __name__ == "__main__":
    data = [3, 6, 8, 10, 1, 2, 1]
    print(f"Original: {data}")
    sorted_data = quick_sort(data)
    print(f"Sorted: {sorted_data}")

Implements the quick sort algorithm using recursion and list comprehensions in Python.

numbers = range(1, 11)
square_dict = {x: x**2 for x in numbers if x % 2 == 0}
print(f"Square dict: {square_dict}")

Using dictionary comprehensions to map squares and filter values.

numbers = range(1, 11)
evens = list(filter(lambda x: x % 2 == 0, numbers))
squares = list(map(lambda x: x**2, evens))
print(f"Evens: {evens}, Squares: {squares}")

Using map and filter functions with lambda expressions.

from functools import reduce
numbers = [1, 2, 3, 4, 5]
sum_numbers = reduce(lambda a, b: a + b, numbers)
print(f"Sum: {sum_numbers}")

Using lambda functions with functools.reduce.

numbers = [1, 2, 2, 3, 3, 4]
squared_set = {x**2 for x in numbers}
print(f"Squared set: {squared_set}")

Using set comprehension to remove duplicates and square numbers.

matrix = [[1,2,3],[4,5,6],[7,8,9]]
flat = [num for row in matrix for num in row]
print(f"Flattened list: {flat}")

Flattening a 2D list using nested list comprehension.

def greet(name: str, greeting: Optional[str] = "Hello") -> None:
    print(f"{greeting}, {name}!")

greet("Alice")
greet("Bob", greeting="Hi")

Defining a function with an optional parameter and default value.

names = ["Alice", "Bob", "Charlie"]
ages = [25, 30, 35]
for name, age in zip(names, ages):
    print(f"{name} is {age} years old")

Using zip to combine two lists and iterate over pairs.

numbers = range(1, 11)
even_squares = [x**2 for x in numbers if x % 2 == 0]
print(f"Even squares: {even_squares}")

Filtering and transforming a list in one comprehension.

def factorial(n: int) -> int:
    if n <= 1:
        return 1
    return n * factorial(n-1)

print(f"Factorial of 5: {factorial(5)}")

Recursive function to compute factorial.