def binary_search(list,item):
	low=0
	high=len(list)-1

	while low <= high:
		mid=(low+high)//2
		guess=list[mid]
		if guess == item:
			return mid
		if guess > item:
			high=mid-1
		else:
			low=mid+1
	return None

my_list=[1,3,4,5,8,9]

print(binary_search(my_list,3))
print(binary_search(my_list,-3))
