--- title: Generators slug: generators category: advanced order: 1 difficulty: advanced estimatedMinutes: 15 prerequisites: - for-loops - defining tags: - generators - yield - iterators --- # Generators Generators are functions that produce a sequence of values **lazily** — one at a time, only when needed. They use `yield` instead of `return`. ## Basic Generator def count_up_to(n): i = 1 while i <= n: yield i i += 1 for num in count_up_to(5): print(num, end=" ") print() ## Why Generators? Generators are memory-efficient because they don't store all values at once: # A list stores everything in memory squares_list = [x**2 for x in range(5)] print(f"List: {squares_list}") # A generator produces values on demand squares_gen = (x**2 for x in range(5)) print(f"Generator: {squares_gen}") # Consume the generator for s in squares_gen: print(s, end=" ") print() ## Generator Expressions Like list comprehensions but with parentheses: # Generator expression — lazy total = sum(x**2 for x in range(1, 11)) print(f"Sum of squares 1-10: {total}") ## Practical Example: Fibonacci def fibonacci(): a, b = 0, 1 while True: yield a a, b = b, a + b # Get first 10 Fibonacci numbers fib = fibonacci() first_ten = [next(fib) for _ in range(10)] print(first_ten) ## Challenges Write a generator `squares(n)` that yields the square of each number from 1 to n. def squares(n): for i in range(1, n + 1): pass # yield the square print(" ".join(str(x) for x in squares(5))) Use `yield i ** 2` inside the loop. def squares(n): for i in range(1, n + 1): yield i ** 2 print(" ".join(str(x) for x in squares(5))) Write a generator `evens(n)` that yields even numbers from 2 up to and including n. def evens(n): pass print(" ".join(str(x) for x in evens(10))) Loop from 2 to n+1 with step 2, yielding each value: `for i in range(2, n+1, 2): yield i` def evens(n): for i in range(2, n + 1, 2): yield i print(" ".join(str(x) for x in evens(10)))