Binary search (python2.7) memo

def binary_search(list, item):
    low = 0                               #Track the search part of the list using low and high
    high = len(list) - 1
    
    while low <= high:
        mid = (low + high) // 2
        guess = list[mid]          #Examine the element in the middle
        if guess == item:        #Detect item
            return mid     #If the answer is correct, mid(index)return it
        if guess > item:    #The number I guessed was too big
            high = mid -1
        else:                   #Was too small
            low = mid + 1
    return None    #If you can't find it, None

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

print binary_search(my_list, 3) #The answer is 3

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