本文介绍Python序列中的字符串。
1. 字符串
字符串支持序列操作。
1.1 string模块预定义字符串
>>> import string
>>> string.ascii_letters
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> string.ascii_lowercase
'abcdefghijklmnopqrstuvwxyz'
>>> string.ascii_uppercase
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> string.digits
'0123456789'
>>> 1.2 普通字符串与Unicode字符串
>>> u'Hello' + ' furzoom'
u'Hello furzoom'
>>> 1.3 只适用于字符串的操作
字符串格式化符号
| 格式化字符 | 转换方式 |
|---|---|
| %c | 转换成字符（ASCII码值，或者长度为一的字符串） |
| %r | 优先用repr()函数进行字符串转换 |
| %s | 优先用str()函数进行字符串转换 |
| %d/%i | 转换成有符号十进制数 |
| %u | 转换成无符号十进制数 |
| %o | 转换成无符号八进制数 |
| %x/%X | 转换成无符号十六进制数 |
| %e/%E | 转换成科学计数法 |
| %f/%F | 转换成浮点数 |
| %g/%G | %e和％f/％E和%F的简写 |
| %% | 转出% |
格式化操作辅助指令
| 符号 | 作用 |
|---|---|
| * | 定义宽度或者小数点精度 |
| - | 左对齐 |
| + | 在正数前显示加号(+) |
| <sp> | 在正数前显示空格 |
| 0 | 显示数字前填充0，而不是空格 |
| # | 在八进制数前显示0，在十六进制前显示0x或者0X |
| (var) | 映射变量(字典参数) |
| m.n | m表示显示的最小总宽度，n是小数点后的位数 |
>>> '%x' % 108
'6c'
>>> '%X' % 108
'6C'
>>> '%#X' % 108
'0X6C'
>>> '%#x' % 108
'0x6c'
>>> '%f' % 1234.567890
'1234.567890'
>>> '%.2f' % 1234.567890
'1234.57'
>>> '%E' % 1234.567890
'1.234568E+03'
>>> '%e' % 1234.567890
'1.234568e+03'
>>> '%g' % 1234.567890
'1234.57'
>>> '%G' % 1234.567890
'1234.57'
>>> '%e' % 111111111111111111111
'1.111111e+20'
>>> 'Welcome to %(website)s, %(name)s' % {'name': 'mn', 'website': 'furzoom.com'}
'Welcome to furzoom.com, mn'
>>> from string import Template
>>> s = Template('There are ${howmany} ${lang} Quotation Symbols')
>>> print s.substitute(lang='Python', howmany=3)
There are 3 Python Quotation Symbols
>>>
>>> print s.substitute(lang='Python')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/string.py", line 172, in substitute
return self.pattern.sub(convert, self.template)
File "/usr/lib/python2.7/string.py", line 162, in convert
val = mapping[named]
KeyError: 'howmany'
>>>
>>> print s.safe_substitute(lang='Python')
There are ${howmany} Python Quotation Symbols
>>> 1.4 原始字符串
>>> '
'
'
'
>>> print '
'
>>> r'
'
'\n'
>>> print r'
'
>>> 1.5 Unicode字符串操作符
他用Unicode原始字符串时，u要出现在r前面。
>>> ur'hello
furzoom'
u'hello\nfurzoom'
>>> ru'hello
mn'
File "<stdin>", line 1
ru'hello
mn'
^
SyntaxError: invalid syntax
>>>2. 内建函数
2.1 标准类型函数与序列操作函数
- cmp()
- len()
- max()
- min()
- enumerate()
- zip()
>>> s1 = 'furzoom'
>>> s2 = 'abcdefg'
>>> cmp(s1, s2)
1
>>> cmp(s2, s1)
-1
>>> cmp(s1, 'furzoom')
0
>>> len(s1)
7
>>> max(s1)
'z'
>>> min(s1)
'f'
>>> us1 = u'furzoom'
>>> len(us1)
7
>>> us1
u'furzoom'
>>> print us1
furzoom
>>> min(us1)
u'f'
>>> max(us1)
u'z'
>>> for i, t in enumerate(s1):
... print i, t
...
0 f
1 u
2 r
3 z
4 o
5 o
6 m
>>> zip(s2, s1)
[('a', 'f'), ('b', 'u'), ('c', 'r'), ('d', 'z'), ('e', 'o'), ('f', 'o'), ('g', 'm')]
>>> 2.2 字符串类型函数
- raw_input()
- str()
- unicode()
- chr()
- unichr()
- ord()
unichr()如果配置为USC2的Unicode，参数范围是range(65535)，如果配置为USC4的Unicode，那么参数范围是range(0x1100000)。
>>> name = raw_input("Enter your name: ")
Enter your name: furzoom MN
>>> name
'furzoom MN'
>>> len(name)
10
>>> unicode(name)
u'furzoom MN'
>>> str(unicode(name))
'furzoom MN'
>>>
>>> isinstance(u' xAB', str)
False
>>> isinstance('mn', unicode)
False
>>> isinstance(u'', unicode)
True
>>> isinstance('mn', str)
True
>>> chr(65)
'A'
>>> ord('a')
97
>>> unichr(12345)
u'u3039'
>>> chr(12345)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: chr() arg not in range(256)
>>> ord(u'uffff')
65535
>>> 3. 字符串内建函数
- string.capitalize()
- string.center(width[, fillchar])
- string.count(sub[, start[, end]]])
- string.decode（[encode[, errors]])
- string.encode([encode[, errors]])
- string.endswith(suffix[, start[, end]]])
- string.expandtabs([tabsize])
- string.find(sub[, start[, end]])
- string.format(*args, **kwargs)
- string.index(sub[, start[, end]])
- string.isalnum()
- string.isalpha()
- string.isdigit()
- string.islower()
- string.isspace()
- string.istitle()
- string.isupper()
- string.istitle()
- string.join(iterable)
- string.ljust(width[, fillchar])
- string.lower()
- string.lstrip([chars])
- string.partition(sep)
- string.replace(old, new[, count])
- string.rfind(sub[, start[, end]])
- string.rindex(sub[, start[, end]])
- string.rjust(width[, fillchar])
- string.rpartition(sep)
- string.rsplit([sep[, maxsplit]])
- string.rstrip([chars])
- string.split([sep[, maxsplit]])
- string.splitlines([keepends])
- string.startswith(prefix[, start[, end]])
- string.strip([chars])
- string.swapcase()
- string.title()
- string.translate(talbe[, deletechars])
- string.upper()
- string.zfill(width)
string.format()将在后面进行介绍。
>>> s = 'welcome to visit furzoom.com'
>>> s.capitalize()
'Welcome to visit furzoom.com'
>>> s.center(50)
' welcome to visit furzoom.com '
>>> s.center(50, '#')
'###########welcome to visit furzoom.com###########'
>>> s.count('om')
3
>>> s.count('om', -10)
2
>>> s.count('om', 0, 10)
1
>>> s.decode()
u'welcome to visit furzoom.com'
>>> s.decode().encode()
'welcome to visit furzoom.com'
>>> s.endswith('com')
True
>>> s.endswith('')
True
>>> s.endswith('mn')
False
>>> s.endswith('co', 0, -1)
True
>>> s1 = '1 23 456 789'
>>> s1.expandtabs()
'1 23 456 789'
>>> s1.expandtabs(4)
'1 23 456 789'
>>> s1.expandtabs(3)
'1 23 456 789'
>>> s1.expandtabs(5)
'1 23 456 789'
>>> s1.expandtabs(6)
'1 23 456 789'
>>> s.find('om')
4
>>> s.find('mn')
-1
>>> s.find('om', 5)
22
>>> s.index('om')
4
>>> s.index('mn')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: substring not found
>>> '234'.isalnum()
True
>>> s.isalnum()
False
>>> ''.isalnum()
False
>>> s.isalpha()
False
>>> 'furzoom'.isalpha()
True
>>> s.isdigit()
False
>>> '234'.isdigit()
True
>>> ''.isdigit()
False
>>> s.islower()
True
>>> '234'.islower()
False
>>> s.isspace()
False
>>> ' '.isspace()
True
>>> s.istitle()
False
>>> 'Welcome To Furzoom'.istitle()
True
>>> s.isupper()
False
>>> 'MN'.isupper()
True
>>> '#'.join([str(i) for i in range(10)])
'0#1#2#3#4#5#6#7#8#9'
>>> s.ljust(40)
'welcome to visit furzoom.com '
>>> s.ljust(40, '#')
'welcome to visit furzoom.com############'
>>> s.lower()
'welcome to visit furzoom.com'
>>> ss = s.center(40)
>>> ss
' welcome to visit furzoom.com '
>>> ss.lstrip()
'welcome to visit furzoom.com '
>>> ss.lstrip(' we')
'lcome to visit furzoom.com '
>>> s.partition('om')
('welc', 'om', 'e to visit furzoom.com')
>>> s.partition('mn')
('welcome to visit furzoom.com', '', '')
>>> s.replace('o', '#')
'welc#me t# visit furz##m.c#m'
>>> s.replace('o', '#', 3)
'welc#me t# visit furz#om.com'
>>> s.rfind('o')
26
>>> s.rfind('o', 25)
26
>>> s.rfind('o', -3)
26
>>> s.rfind('o', -3, -20)
-1
>>> s.rfind('o', 5, 15)
9
>>> s.rindex('om')
26
>>> s.rjust(40)
' welcome to visit furzoom.com'
>>> s.rjust(40, '#')
'############welcome to visit furzoom.com'
>>> s.rpartition('oom')
('welcome to visit furz', 'oom', '.com')
>>> s.rsplit()
['welcome', 'to', 'visit', 'furzoom.com']
>>> s.rsplit(' ', 2)
['welcome to', 'visit', 'furzoom.com']
>>> ss.rstrip()
' welcome to visit furzoom.com'
>>> ss.rstrip(' m')
' welcome to visit furzoom.co'
>>> 'ab
de fg
hi
'.splitlines()
['ab', '', 'de fg', 'hi']
>>> 'ab
de fg
hi
'.splitlines(True)
['ab
', '
', 'de fg
', 'hi
']
>>> ''.splitlines()
[]
>>> ''.split('
')
['']
>>> 'line
'.split('
')
['line', '']
>>> 'line
'.splitlines()
['line']
>>> s.startswith('wel')
True
>>> s.startswith(' ')
False
>>> ss.strip()
'welcome to visit furzoom.com'
>>> ss.strip(' wm')
'elcome to visit furzoom.co'
>>> s.swapcase()
'WELCOME TO VISIT FURZOOM.COM'
>>> s.title()
'Welcome To Visit Furzoom.Com'
>>> s.title().swapcase()
'wELCOME tO vISIT fURZOOM.cOM'
>>> s.translate(None, 'aeiou')
'wlcm t vst frzm.cm'
>>> import string
>>> s.translate(string.maketrans('aeiou', '12345'))
'w2lc4m2 t4 v3s3t f5rz44m.c4m'
>>> s.upper()
'WELCOME TO VISIT FURZOOM.COM'
>>> s.zfill(40)
'000000000000welcome to visit furzoom.com'4. 字符串特有性质
4.1 转义字符
| 转义字符 | 十六进制 |
|---|---|
| 0x00 | |
| a | 0x07 |
| 0x08 | |
| 0x09 | |
| 0x0A | |
| v | 0x0B |
| f | 0x0C |
| 0x0D | |
| e | 0x1B |
| ” | 0x22 |
| ’ | 0x27 |
| \ | 0x5C |
>>> print 'aaabb'
abb
>>> print 'aaaaaaa
bbc'
bbcaaaa4.2 三引号
使用三引号，字符串可以包含换行符、制表符等其他特殊字符。常常在需要包含HTML和SQL语句时使用。
4.3 字符串是不可变数据类型
当修改一个字符串时，都是新建了一个字符串。