利用Python写二分查找算法

#!/usr/bin/env python
# _*_ encoding:utf-8 _*_

def binary_search(list,item):
    low = 0
    high = len(list)-1
    while low<=high:
        mid = (low+high)//2   # python2: mid = (low+high)/2
        print(mid)
        guess = list[mid]
        if guess>item:
            high = mid-1
        elif guess<item:
            low = mid+1
        else:
            return mid
    return None
mylist = [1,3,5,7,9,10,11,13]
print(binary_search(mylist,5))