4.3. 数据类型：拿什么来装数据？

4.3.1. 序列概述

>>>edward = ['Edward Gumby', 42]
>>>john = ['John Smith', 50]
>>>database = [edward, john]
database

4.3.2. 通用的序列操作

4.3.2.1. 索引

>>> greeting = 'Hello'
>>> greeting[0]
'H'

>>> greeting[-1]
'o'

>>> 'Hello'[1]
'e'

>>> fourth = input('Year: ')[3]
Year: 2005
>>> fourth
'5'

具体事例

# 将以数指定年、月、日的日期打印出来
months = [
        'January',
        'February',
        'March',
        'April',
        'May',
        'June',
        'July',
        'August',
        'September',
        'October',
        'November',
        'December'
]
# 一个列表，其中包含数1～31对应的结尾
endings = ['st', 'nd', 'rd'] + 17 * ['th'] \
                + ['st', 'nd', 'rd'] + 7 * ['th'] \
                + ['st']
year = input('Year: ')
month = input('Month (1-12): ')
day = input('Day (1-31): ')
month_number = int(month)
day_number = int(day)
# 别忘了将表示月和日的数减1，这样才能得到正确的索引
month_name = months[month_number-1]
ordinal = day + endings[day_number-1]
print(month_name + ' ' + ordinal + ', ' + year)
这个程序的运行情况类似于下面这样：
Year: 1974
Month (1-12): 8
Day (1-31): 16
August 16th, 1974

4.3.2.2. 切片操作

>>> tag = '<a href="http://www.python.org">Python web site</a>'
>>> tag[9:30]
'http://www.python.org'
>>> tag[32:-4]
'Python web site'

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

具体事例

# 从类似于http://www.something.com的URL中提取域名
url = input('Please enter the URL:')
domain = url[11:-4]
print("Domain name: " + domain)
这个程序的运行情况类似于下面这样：
Please enter the URL: http://www.python.org
Domain name: python

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

4.3.2.3. 序列相加

>>> [1, 2, 3] + [4, 5, 6]
[1, 2, 3, 4, 5, 6]
>>> 'Hello,' + 'world!'
'Hello, world!'
>>> [1, 2, 3] + 'world!'
Traceback (innermost last):
File "<pyshell>", line 1, in ?
[1, 2, 3] + 'world!'
TypeError: can only concatenate list (not "string") to list

4.3.2.4. 乘法

>>> 'python' * 5
'pythonpythonpythonpythonpython'
>>> [42] * 10
[42, 42, 42, 42, 42, 42, 42, 42, 42, 42]

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

具体事例

# 在位于屏幕中央且宽度合适的方框内打印一个句子
sentence = 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 + ' |')
print(' ' * left_margin + '| ' + sentence + ' |')
print(' ' * left_margin + '| ' + ' ' * text_width + ' |')
print(' ' * left_margin + '+' + '-' * (box_width-2) + '+')
print()
这个程序的运行情况类似于下面这样：
Sentence: He's a very naughty boy!
+-----------------------------+
|                             |
| He's a very naughty boy!    |
|                             |
+-----------------------------+

4.3.2.5. 成员资格

>>> permissions = 'rw'
>>> 'w' in permissions
True
>>> 'x' in permissions
False
>>> users = ['mlh', 'foo', 'bar']
>>> input('Enter your user name: ') in users
Enter your user name: mlh
True
>>> subject = '$$$ Get rich now!!! $$$'
>>> '$$$' in subject
True

4.3.2.6. 长度、最小值和最大值

>>> numbers = [100, 34, 678]
>>> len(numbers)
3
>>> max(numbers)
678
>>> min(numbers)
34
>>> max(2, 3)
3
>>> min(9, 3, 2, 5)
2

4.3.3. 列表：Python的助力

4.3.3.1. 函数list

>>> list('Hello')
['H', 'e', 'l', 'l', 'o']

4.3.3.2. 基本的列表操作

4.3.3.2.1. 修改列表

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

4.3.3.2.2. 删除元素

>>> names = ['Alice', 'Beth', 'Cecil', 'Dee-Dee', 'Earl']
>>> del names[2]
>>> names
['Alice', 'Beth', 'Dee-Dee', 'Earl']

4.3.3.2.3. 给切片赋值

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

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

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

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

4.3.3.3. 列表方法

4.3.3.3.1. append

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

4.3.3.3.2. clear

>>> lst = [1, 2, 3]
>>> lst.clear()
>>> lst
[]

4.3.3.3.3. copy

>>> a = [1, 2, 3]
>>> b = a.copy()
>>> b[1] = 4
>>> a
[1, 2, 3]

4.3.3.3.4. count

>>> ['to', 'be', 'or', 'not', 'to', 'be'].count('to')
2
>>> x = [[1, 2], 1, 1, [2, 1, [1, 2]]]
>>> x.count(1)
2
>>> x.count([1, 2])
1

4.3.3.3.5. extend

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

4.3.3.3.6. index

>>> knights = ['We', 'are', 'the', 'knights', 'who', 'say', 'ni']
>>> knights.index('who')
4
>>> knights.index('herring')
Traceback (innermost last):
File "<pyshell>", line 1, in ?
knights.index('herring')
ValueError: list.index(x): x not in list
>>> knights[4]
'who'

4.3.3.3.7. insert

>>> numbers = [1, 2, 3, 5, 6, 7]
>>> numbers.insert(3, 'four')
>>> numbers
[1, 2, 3, 'four', 5, 6, 7]

4.3.3.3.8. pop

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

4.3.3.3.9. remove

>>> x = ['to', 'be', 'or', 'not', 'to', 'be']
>>> x.remove('be')
>>> x
['to', 'or', 'not', 'to', 'be']
>>> x.remove('bee')
Traceback (innermost last):
File "<pyshell>", line 1, in ?
x.remove('bee')
ValueError: list.remove(x): x not in list

4.3.3.3.10. reverse

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

4.3.3.3.11. sort

>>> x = [4, 6, 2, 1, 7, 9]
>>> x.sort()
>>> x
[1, 2, 4, 6, 7, 9]

>>> x = ['aardvark', 'abalone', 'acme', 'add', 'aerate']
>>> x.sort(key=len)
>>> x
['add', 'acme', 'aerate', 'abalone', 'aardvark']

>>> x = [4, 6, 2, 1, 7, 9]
>>> x.sort(reverse=True)
>>> x
[9, 7, 6, 4, 2, 1]

4.3.3.4. 本章介绍的新函数

函数	描述
len(seq)	返回序列的长度
list(seq)	将序列转换成列表
max(args)	返回序列或一组参数中的最大值
min(args)	返回序列和一组参数中的最小值
reversed(seq)	让你能够反向迭代序列
sorted(seq)	返回一个有序列表，其中包含指定序列中的所有元素
tuple(seq)	将序列转换为元组