二分查找

#coding:utf-8
def binary_search(list, item):
    low = 0
    high = len(list) - 1
    while low <= high:
        mid = (high - low) / 2 + low    # 避免(high + low) / 2溢出
        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]
print binary_search(mylist, 3)

参考: http://blog.csdn.net/u013205877/article/details/76411718