第02章: 列表和数组

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在Python中最基本的数据结构是序列，每个元素分配一个序号，即元素的序号，也即索引。注意，需要从0开始，第一位0，第二位为1，依次类推. Python包括: 字符串，列表，元祖，字典 这四种常用数据结构，或者说四种序列，其中元祖为不可变序列.

列表和元祖的主要区别

• 列表可变，而元祖不可变             >>>list1 = [‘Tom‘,40]
• 所以元祖: 主要用于存储不变的数据   >>>

>>> tuple1 = (130,131,132,133,134)
>>> tuple1[0]=135


Traceback (most recent call last):
  File "<pyshell#199>", line 1, in <module>
    tuple1[0]=135
TypeError: 'tuple' object does not support item assignment
>>> list = ['Tom',40]
>>> list
['Tom', 40]
>>> list[0]='Jerry'
>>> list
['Jerry', 40]

再比如:要建个记录姓名，和年龄的元祖，可以这样:

>>> edward = ['Edward Gumby',40]
>>> john   = ['John Smith',50]
>>> database = [edward,john]
>>> database
[['Edward Gumby', 40], ['John Smith', 50]]

通用序列可做的操作:

• 索引
• 切片
• 增加元素
• 删除元素
• 更新元素
• 查找元素(检查某个元素是否是序列中的一员)
• 序列长度 
• 最大值
• 最小值
• 其他内建函数

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索引

>>> greeting = ‘Hello World!‘
>>> greeting[0]
‘H‘
>>> greeting[-1]
‘!‘

如果只对年份的第四位感兴趣，可以这样:

>>> fouth = raw_input(‘Year: ‘)[3]
Year: 2008
>>> fouth
‘8‘

<span style="font-size:18px;">#Filename: showmonth.py

months = [
    'January',
    'February',
    'March',
    'April',
    'May',
    'June',
    'July',
    'August',
    'September',
    'October',
    'November',
    'December'
]

year    = raw_input('Year: ')
month   = raw_input('Month(1-12): ')
day     = raw_input('Day(1-31): ')

endings = ['st','nd','rd'] + 17*['th'] +           ['st','nd','rd'] + 07*['th'] +           ['st']

month_number = int(month)
day_number   = int(day)

month_name   = months[month_number-1]
ordinal      = day + endings[day_number]

print month_name[:3] + ' ' + ordinal + ', ' + year

# 输出结果
D:\>python showmonth.py
Year: 2014
Month(1-12): 09
Day(1-31): 13
Sep 13th, 2014
</span>

切片

>>> tag = ‘<a href=http://www.mamicode.com/"http://www.python.org">Python Web Site‘
>>> tag[9:30]
‘http://www.python.org‘

>>> tag[32:-4]
‘Python Web Site‘

#输出最后三位,如要统计最后一位，其下一位必须被列出
>>> numbers[7:10]
[8, 9, 10]
#或者直接到:表示后面的
>>> numbers[7:]
[8, 9, 10]
#[:]或者[::]表示所有的
>>> numbers[-3:]
[8, 9, 10]
#倒序输出，步幅为-1，即从右到左
>>> numbers[-1:-4:-1] 
[10, 9, 8]
#输出开始的三位
>>> numbers[:3]
[1, 2, 3]
#输出所有的
>>> numbers[:]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
#输出所有的另一种写法
>>> numbers[::]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

例子:取http://www.something.com中的域名:

url = raw_input('Enter Url Here:')
Enter Url Here:http://www.sohu.com
print "Domain is:" + url[11:-4]
Domain is:sohu

更大步长

>>> numbers[0:10:1]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> numbers[0:10:2]
[1, 3, 5, 7, 9]
>>> numbers[::4]
[1, 5, 9]
>>> numbers[8:3:-1]
[9, 8, 7, 6, 5]
>>> numbers[10:0:-2]
[10, 8, 6, 4, 2]
>>> numbers[0:10:-2]
[]
>>> numbers[::-2]
[10, 8, 6, 4, 2]
>>> numbers[5::-2]
[6, 4, 2]

>>> [1,2]+[3,4]
[1, 2, 3, 4]
>>> 'Hello,'+'World!'
'Hello,World!'
>>> [1,2]+'Hello'


Traceback (most recent call last):
  File "<pyshell#253>", line 1, in <module>
    [1,2]+'Hello'
TypeError: can only concatenate list (not "str") to list

乘法

#列表倍乘

>>> [0]*10
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
#字符串倍乘
>>> 'python'*5
'pythonpythonpythonpythonpython'

>>> seq = [None]*10
>>> seq
[None, None, None, None, None, None, None, None, None, None]

#以正确的宽度在居中的“盒子”内打印一个句子

sentence     = raw_input("Sentence:")

screen_width = 80
text_width   = len(sentence)
box_width    = text_width +6

left_margin  = (screen_width-box_width)/2

print 
print ' '*left_margin + '+' +'-'*(box_width-2)   + '+'
print ' '*left_margin + '| ' +' '*(text_width+2) + ' |'
print ' '*left_margin + '| ' + sentence  + ' '*2 + ' |'
print ' '*left_margin + '| ' +' '*(text_width+2) + ' |'
print ' '*left_margin + '+' +'-'*(box_width-2)   + '+'
print

D:\Work\Python>python showmonth.py
Sentence:I Love Python

                              +-----------------+
                              |                 |
                              | I Love Python   |
                              |                 |
                              +-----------------+

成员资格:

用in运算符号判断成员资格，在则为True,不在则为假:

>>> permissions='rw'
>>> 'w' in permissions
True
>>> 'x' in permissions
False
users=['root','test','guest']
print raw_input('Name:') in users
D:\>python showmonth.py
Name:root
True
>>> subject = '$$$ Get Rich Now! $$$'
>>> '$$$' in subject
True

database=[
    ['root','1234'],
    ['test','5678'],
    ['book','9012']
    ]

user = raw_input('Enter user: ')
puid = raw_input('Enter puid: ')

if [user,puid] in database:
    print 'Access Granted.'
else:
    print 'User or Pid not correct.'

长度，最大值，最小值

>>> n = [78,23,64]
>>> len(n);max(n);min(n)
3
78
23
可对多值进行比较
>>> min(9,3,2,5) ; max(9,3,2,5)
2
9

list函数

#将字符串转为由单个字符的列表
>>> list('hello')
['h', 'e', 'l', 'l', 'o']
#将由字符组成的列表转成字符串
>>> list1=['d','a','y']
>>> ''.join(list1)
'day'

基本操作

#更新元素，赋值

>>> x = [0,1,2]
>>> x[0]=8
>>> x
[8, 1, 2]

>>> x[3]=3

Traceback (most recent call last):
  File "<pyshell#40>", line 1, in <module>
    x[3]=3
IndexError: list assignment index out of range

>>> names=['Jerry','John','Jack','Alice']
>>> del names[3]
>>> names
['Jerry', 'John', 'Jack']

>>> s = '1234'
>>> def sum1(x,y):
	return x+y

>>> sum1(1,2)
3
>>> del s; del sum1
>>> s

Traceback (most recent call last):
  File "<pyshell#51>", line 1, in <module>
    s
NameError: name 's' is not defined
>>> sum1(1,2)

Traceback (most recent call last):
  File "<pyshell#52>", line 1, in <module>
    sum1(1,2)
NameError: name 'sum1' is not defined

分片赋值

#同长度赋值

>>> name=list('Perl')
>>> name
['P', 'e', 'r', 'l']
>>> name[2:]='ar'
>>> name
['P', 'e', 'a', 'r']

>>> name=list('Perl')
>>> name
['P', 'e', 'r', 'l']
>>> name[1:]='ython'
>>> name
['P', 'y', 't', 'h', 'o', 'n']

>>> number = [1,5]
>>> number[1:1]=[2,3,4]
>>> number
[1, 2, 3, 4, 5]

>>> number = [1,2,3,4,5]
>>> number[1:4]=[]
>>> number
[1, 5]
等价于 del number[1:4]

列表方法

append: 末尾添加

>>> num = [1,2,3]
>>> num.append(4)
>>> num
[1, 2, 3, 4]

>>> ['to','re','be','hi','to'].count('to')
2
>>> list1 = [[1,2],1,1,2,2,[2,1]]
>>> list1.count(1)
2
>>> list1.count([1,2])
1

>>> a = [1,2,3]
>>> b = [4,5,6]
>>> a.extend(b)
>>> a
[1, 2, 3, 4, 5, 6]

>>> a = [1,2,3]
>>> b = [4,5,6]
>>> a + b
[1, 2, 3, 4, 5, 6]
>>> a
[1, 2, 3]

>>> a = [1,2,3]
>>> a[len(a):] = [4,5,6]
>>> a
[1, 2, 3, 4, 5, 6]

>>> list1=['I','love','python','i','love','perl']
>>> list1.index('love')
1
>>> list1[1]
'love'
#如果没有的话，则会返回不在列的异常
>>> list1.index('java')

Traceback (most recent call last):
  File "<pyshell#54>", line 1, in <module>
    list1.index('java')
ValueError: 'java' is not in list

>>> numbers = [1,2,3,5,6]
>>> numbers.insert(3,'four')
>>> numbers
[1, 2, 3, 'four', 5, 6]
#当然也可以用切片的方式来完成，但可读性不如insert
>>> numbers = [1,2,3,5,6]
>>> numbers[3:3]=['four']
>>> numbers
[1, 2, 3, 'four', 5, 6]

pop: 移除列表中的元素，默认的话是最后一位 

Note:

• pop是即能修改元素又能返回列表值(None除外)的函数
• 可以append(pop(0))来实现FIFO功能
• 也可以用insert(0...)配合pop来实现FIFO或者collection中的deque对象

>>> x = [1,2,3]
>>> x.pop()
3
>>> x
[1, 2]
>>> x.pop(0)
1
>>> x
[2]

pop可以实现栈(FIFO:先进先出,入栈(push)、出栈(pop))
pop 保持不变，push等价于append
>>> x = [1,2,3]
>>> x.append(x.pop())
>>> x
[1, 2, 3]

remove: 移除匹配中第一个元素值

Note:和pop相对，都是操作第一个匹配值，但remove没有返回项
>>> x =['to','be','or','not','to','be']
>>> x.remove('be')
>>> x
['to', 'or', 'not', 'to', 'be']

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<<Python基础教程>>学习笔记 | 第02章 | 列表和数组