二分查找有序序列

# coding=utf-8
def findnumber(lists,num):
    i=0
    j=len(lists)-1
    while i<=j:
        mid=(i+j)//2
        if lists[mid] > num:
            j=mid-1
        elif lists[mid] < num:
            i=mid+1
        else:
            return mid+1
    return -1
if __name__ == '__main__':
    lists=[1,3,5,7,9]
    print(findnumber(lists,9))