1 def binary_search(list, item):
 2     low = 0
 3     high = len(list)-1
 4 
 5     while low <= high:
 6         mid = (low + high)
 7         guess = list[mid]
 8         if guess == item:
 9             return mid
10         if guess > item:
11             high = mid-1
12         else:
13             low = mid + 1
14     return None
15 
16 my_list = [1, 3, 5, 7, 9]
17 print (binary_search(my_list, 3)) # => 1