6 List和tuple、序列对象

内置数据结构

• list

  Python内置的一种数据类型是列表：list。list是一种有序的集合，可以随时添加和删除其中的元素。

  • 具有顺序的一组对象
  • 可以随意访问其中的任意位置
  • 可以添加和删除
  • 其中的元素不需要是同类型，但最好是一组同质对象

import sys
# shoplist = ['apple', 'mango','carrot', 'banana']
shoplist = list()
shoplist.append('apple')
shoplist.append('mango')
shoplist.append('carrot')
shoplist.append('banana')
print('shoplist len is {}'.format(len(shoplist)))
sys.stdout.write('These items are:')
for item in shoplist:
    sys.stdout.write(str(item) + '')
print('\nI also want to buy rice.')
shoplist.append('rice')
print('New shoplist is : {}'.format(shoplist))
shoplist.sort()
print('Sorted list is {}'.format(shoplist))
print('the first item is {}'.format(shoplist[0]))
-----------------------------------------------------
shoplist len is 4
These items are:applemangocarrotbanana
I also want to buy rice.
New shoplist is : ['apple', 'mango', 'carrot', 'banana', 'rice']
Sorted list is ['apple', 'banana', 'carrot', 'mango', 'rice']
the first item is apple

• tuple

  • 具有顺序的一组对象【同list】
  • 可以随意访问其中的任意位置【同list】
  • 不可以添加和删除
  • 其中的元素不需要是同类型

  tuple和list非常类似，但是tuple一旦初始化就不能修改,它也没有append()，insert()这样的方法。其他获取元素的方法和list是一样的，你可以正常地使用[0]，[-1],但不能赋值成另外的元素。uple不可变，所以代码更安全。如果可能，能用tuple代替list就尽量用tuple。

  定义一个只有1个元素的tuple

>>> t = (1,)
>>> t
(1,)

如果定义成这样：

>>> t = (1)
>>> t
1

定义的不是tuple，是1这个数！这是因为括号()既可以表示tuple，又可以表示数学公式中的小括号，这就产生了歧义，因此，Python规定，这种情况下，按小括号进行计算，计算结果自然是1。

Python在显示只有1个元素的tuple时，会加一个逗号,，以免你误解成数学计算意义上的括号。

• 操作序列对象
  • 通过[]访问
  • 通过[]设定值
  • 通过for枚举
  • 通过[：]访问
  • 通过[:]设定值
  • 通过[：：]设定步进

zoo = ('python', 'elephant', 'penguin') # 用（）来表示 
print('number is {}'.format(len(zoo)))
new_zoo = 'monkey', 'camel', zoo #可以省略（）
print ('new number is {}'.format(len(new_zoo))) 
print('All animals in new zoo are {}'.format(new_zoo))
print('animals are from old zoo are {}'.format(new_zoo[2]))
print('Number of animals in new zoo is {}'.format(len(new_zoo)-1+len(new_zoo[2])))
-----------------------------------------------
number is 3
new number is 3
All animals in new zoo are ('monkey', 'camel', ('python', 'elephant', 'penguin'))
animals are from old zoo are ('python', 'elephant', 'penguin')
Number of animals in new zoo is 5

r = 1, 2, 3 #另一种写法
r
print(r)
a, b, c = r
print(a)
print(b)
print(c)
------------------------
(1, 2, 3)
1
2
3

def f():
    return (1, 2, 3)
a, b, c = f()
print(a)
print(b)
print(c)
----------------------
1
2
3

print(a)
print(b)
a, b = b, a # 无中间变量翻转对象
print(a)
print(b)
-------------------------------
2
1
1
2

list和tuple是Python内置的有序集合，一个可变，一个不可变。根据需要来选择使用它们。

shoplist =['apple', 'banana', 'carrot', 'mango', 'rice']
print('0 is {}'.format(shoplist[0]))
print('1 is {}'.format(shoplist[1]))
print('2 is {}'.format(shoplist[2]))
print('3 is {}'.format(shoplist[3]))
print('4 is {}'.format(shoplist[4]))
print('-1 is {}'.format(shoplist[-1]))
print('-2 is {}'.format(shoplist[-2]))
print('-3 is {}'.format(shoplist[-3]))
print('-4 is {}'.format(shoplist[-4]))
print('-5 is {}'.format(shoplist[-5]))
print('0 to 3 is {}'.format(shoplist[0:3]))
print('1  to end is {}'.format(shoplist[1: ]))
print('2 to -1 is {}'.format(shoplist[2: -1]))
print('start to end  is {}'.format(shoplist[:]))
---------------------------------------------------
0 is apple
1 is banana
2 is carrot
3 is mango
4 is rice
-1 is rice
-2 is mango
-3 is carrot
-4 is banana
-5 is apple
0 to 3 is ['apple', 'banana', 'carrot']
1  to end is ['banana', 'carrot', 'mango', 'rice']
2 to -1 is ['carrot', 'mango']
start to end  is ['apple', 'banana', 'carrot', 'mango', 'rice']

• dict
  Python内置了字典：dict的支持，dict全称dictionary，在其他语言中也称为map，使用键-值（key-value）存储，具有极快的查找速度。

• set
  set和dict类似，也是一组key的集合，但不存储value。由于key不能重复，所以，在set中，没有重复的key。

• string

name = 'swaroop'
print('Character 0 is {}'.format(name[0]))
print('Character 1 to 3 is {}'.format(name[1: 3]))
print('Character 2 to end  is {}'.format(name[2: ]))
print('Character 2 to -1 is {}'.format(name[ 2: -1]))
print('Character start  to end is {}'.format(name[:]))
print('reversed characters  is {}'.format(name[::-1]))
-----------------------------------------------------
Character 0 is s
Character 1 to 3 is wa
Character 2 to end  is aroop
Character 2 to -1 is aroo
Character start  to end is swaroop
reversed characters  is pooraws

实战练习

#练习
# 1. 建立一个list， 内容为10以内所有的质数
primes = [2, 3, 5, 7]

# 2.计算出100内所有质数的列表
primes = [2, 3, 5, 7]
for i in range(10, 100):
    prime = True
    for j in primes: 
        if i % j ==0:
            prime = False
            break
    if prime:
        primes.append(i)
print(primes)
----------------------------
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

primes = []
l = list(range(2, 100))
while l:
    j = l.pop(0)
    primes.append(j)
    i = 2
    while j * i <= 100:
            if j * i in l:
                l.remove(j * i)
            i += 1
print(primes)

# 3.将这个列表转为tuple
tuple(primes)
--------------
# 4.根据上面的tuple， 获得反转的tuple
tuple(reversed(tuple(primes)))

# 5.将一个list分为两个： 第一个list拥有原本list前一半的反向， 第二个list拥有原本list后一半的反向
list(reversed(primes[:len(primes) //2])), list(reversed(primes[len(primes) // 2: ]))
-----------------------------------------------
([37, 31, 29, 23, 19, 17, 13, 11, 7, 5, 3, 2],
 [97, 89, 83, 79, 73, 71, 67, 61, 59, 53, 47, 43, 41])

primes[len(primes) // 2:: -1 ], primes[:len(primes) //2 : -1]
--------------------------------------
([41, 37, 31, 29, 23, 19, 17, 13, 11, 7, 5, 3, 2],
 [97, 89, 83, 79, 73, 71, 67, 61, 59, 53, 47, 43])