python//Jan.18th,2020//二分查找

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=[1,3,5,7,9]
s=binary_search(my_list,5)
print(s)