def sequentialSearch(items, target):
  for item in items:
    if item == target:
      return True
  return False

def orderedSequentialSearch(items, target):
  for item in items:
    if item == target:
      return True
    elif item > target:
      break
  return False

def iterativeBinarySearch(items, target):
  first = 0
  last = len(items) - 1
  while first <= last:
    middle = (first + last) // 2
    if target == items[middle]:
      return True
    elif target < items[middle]:
      last = middle - 1
    else:
      first = middle + 1
  return False

def recursiveBinarySearch(items, target):
  if len(items) == 0:
    return False
  else:
    middle = len(items) // 2
    if target == items[middle]:
      return True
    elif target < items[middle]:
      return recursiveBinarySearch(items[:middle], target)
    else:
      return recursiveBinarySearch(items[middle+1:], target)

搜索算法          时间复杂度
-----------------------------------
sequentialSearch      O(n)
-----------------------------------
orderedSequentialSearch  O(n) 
-----------------------------------
iterativeBinarySearch   O(log n)
-----------------------------------
recursiveBinarySearch   O(log n)
-----------------------------------
in             O(n)

#!/usr/bin/env python
# -*- coding: utf-8 -*-
def test_print(algorithm, listname, target):
  print(' %d is%s in %s' % (target, '' if algorithm(eval(listname), target) else ' not', listname))
if __name__ == '__main__':
  testlist = [1, 2, 32, 8, 17, 19, 42, 13, 0]
  orderedlist = sorted(testlist)
  print('sequentialSearch:')
  test_print(sequentialSearch, 'testlist', 3)
  test_print(sequentialSearch, 'testlist', 13)
  print('orderedSequentialSearch:')
  test_print(orderedSequentialSearch, 'orderedlist', 3)
  test_print(orderedSequentialSearch, 'orderedlist', 13)
  print('iterativeBinarySearch:')
  test_print(iterativeBinarySearch, 'orderedlist', 3)
  test_print(iterativeBinarySearch, 'orderedlist', 13)
  print('recursiveBinarySearch:')
  test_print(recursiveBinarySearch, 'orderedlist', 3)
  test_print(recursiveBinarySearch, 'orderedlist', 13)

$ python testbasicsearch.py
sequentialSearch:
 3 is not in testlist
 13 is in testlist
orderedSequentialSearch:
 3 is not in orderedlist
 13 is in orderedlist
iterativeBinarySearch:
 3 is not in orderedlist
 13 is in orderedlist
recursiveBinarySearch:
 3 is not in orderedlist
 13 is in orderedlist