（非递归实现）

def binary_search(alist, item):      first = 0      last = len(alist)-1      while first<=last:          midpoint = (first + last)/2          if alist[midpoint] == item:              return True          elif item < alist[midpoint]:              last = midpoint-1          else:              first = midpoint+1    return Falsetestlist = [0, 1, 2, 8, 13, 17, 19, 32, 42,]print(binary_search(testlist, 3))print(binary_search(testlist, 13))

（递归实现）

def binary_search(alist, item):    if len(alist) == 0:        return False    else:        midpoint = len(alist)//2        if alist[midpoint]==item:          return True        else:          if item

• 最优时间复杂度：O(1)
• 最坏时间复杂度：O(logn)

二分查找又称折半查找，优点是比较次数少，查找速度快，平均性能好；其缺点是要求待查表为有序表，且插入删除困难。