binary_search

binary_search.py

def binary_search(lst, item):
	low = 0
	high = len(lst) - 1
	
	while low <= high:
		mid = (low + high) // 2
		guess = lst[mid]
		if guess == item:
			return mid
		if guess > item:
			high = mid - 1
		else:
			low = mid + 1
	return None

my_list = [1, 3, 5, 7, 9]

print(binary_search(my_list, 3)) # => 1
print(binary_search(my_list, -1)) # => None