Python序列——字符串

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

>>> ‘%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

>>> ‘\n‘
‘\n‘
>>> print ‘\n‘


>>> r‘\n‘
‘\\n‘
>>> print r‘\n‘
\n
>>> 

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\nfurzoom‘
u‘hello\\nfurzoom‘
>>> ru‘hello\nmn‘
  File "<stdin>", line 1
    ru‘hello\nmn‘
                ^
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‘\0xAB‘, 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\t23\t456\t789‘
>>> 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
>>> ‘ \t‘.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\n\nde fg\rhi\r\n‘.splitlines()
[‘ab‘, ‘‘, ‘de fg‘, ‘hi‘]
>>> ‘ab\n\nde fg\rhi\r\n‘.splitlines(True)
[‘ab\n‘, ‘\n‘, ‘de fg\r‘, ‘hi\r\n‘]
>>> ‘‘.splitlines()
[]
>>> ‘‘.split(‘\n‘)
[‘‘]
>>> ‘line\n‘.split(‘\n‘)
[‘line‘, ‘‘]
>>> ‘line\n‘.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

>>> print ‘aaa\b\bbb‘
abb
>>> print ‘aaaaaaa\rbbc‘
bbcaaaa

4.2 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。