我要评论1.序列
python有多种内建的序列，所有序列都可以做某些特定的操作，大致上常用的是：加，乘，索引，分片以及检查某个元素是否属于序列的成员。 在这里我们重点讨论两种，字典与列表。并且只讨论其索引效率
2. 列表
列表是python中最具灵活性的有序集合对象类型，其属性：
1. 任意对象的有序集合
2. 通过偏移读取
3. 可变长度、异构以及任意嵌套
4. 属于可变序列的分类
5. 对象引用数组
3. 字典
除了列表外，字典是python中最具灵活性的内置数据结构类型，其属性：
1. 通过键而不是偏移量来读取
2. 任意对象的无序集合（键的hash值存在有序）
3. 可变长、异构以及任意嵌套
4. 属于可映射类型
5. 对象引用表（散列表）
在python中，字典是通过哈希表实现的。也就是说，字典是一个数组，而数组的索引是键经过哈希函数处理后得到的。哈希函数的目的是使键均匀地分布在数组中。
4. 索引效率分析
通过上述可以简单地了解字典和列表的区别，列表是根据偏移量来读取的，字典是根据键的hash来读取的。
通过实验来测试其索引效率：
#!/usr/bin/env python
# -*- coding:utf-8 -*-
###############################################
# file name : test.py
# author : younger liu
# mail : lewiyon@126.com
# created time: tue 19 jun 2018 08:58:42 am cst
# description :
###############################################
import time
import random
import string
max_count = 1000000
def test_dict(data, key=none):
b_time = int(time.time()*1000*1000)
data.get(key)
a_time = int(time.time()*1000*1000)
print("elapsed time %d us to query [%s]" % (a_time - b_time, key))
def test_array(data, key=none):
b_time = int(time.time()*1000*1000)
for ele in data:
if ele == key:
break
continue
a_time = int(time.time()*1000*1000)
print("elapsed time %d us to query [%s]" % (a_time - b_time, key))
def gen_arr():
arr = []
for i in range(max_count):
ele = ''.join(random.sample(string.ascii_letters + string.digits, 8))
arr.append(ele)
if i == 0:
first = ele
elif i == max_count - 1:
last = ele
return arr, first, last
def gen_dict():
dict = {}
for i in range(max_count):
ele = ''.join(random.sample(string.ascii_letters + string.digits, 8))
dict[ele] = ele
if i == 0:
first = ele
elif i == max_count -1:
last = ele
return dict, first, last
if __name__ == '__main__':
arr, first_ele, last_ele = gen_arr()
print("-----query first ele in array-------")
test_array(arr, first_ele)
print("-----query last ele in array-------")
test_array(arr, last_ele)
print("-----query ele not in array-------")
test_array(arr, '111111')
dict, first_key, last_key = gen_dict()
print("-----query first generated ele in dict-------")
test_dict(dict, first_key)
print("-----query last generated ele in dict-------")
test_dict(dict, last_key)
print("-----query ele not in dict-------")
test_dict(dict, '111111')运行结果如下：
-----query first ele in array-------
elapsed time 10 us to query [drp3aezq]
-----query last ele in array-------
elapsed time 37236 us to query [6agsbq37]
-----query ele not in array-------
elapsed time 38666 us to query [111111]
-----query first generated ele in dict-------
elapsed time 12 us to query [dkyn2xjl]
-----query last generated ele in dict-------
elapsed time 3 us to query [brncewp2]
-----query ele not in dict-------
elapsed time 2 us to query [111111]
多次运行，其结果相差不多
由此可见，字典的索引效率要远远大于列表
总结
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