Python Strings笔记

Table of Contents

• 1 %
• 2 不言而喻
• 3 find()
• 4 replace()
• 5 split() rsplit()
• 6 strip rstrip lstrip
• 7 center() ljust() rjust()
• 8 partition() rpartition()
• 9 isdigit() isnumeric()
• 10 swapcase()
• 11 zfill()
• 12 expandtabs()
• 13 isalpha isdigit isalnum islower isspace istitle isupper istitle title capitalize
• 14 maketrans translate
• 15 format()
  • 15.1 基本格式
  • 15.2 Accessing arguments by potition:
  • 15.3 Accessing arguments by name:
  • 15.4 Accessing arguments' attributes:
  • 15.5 Accessing argument's items:
  • 15.6 !s !r
  • 15.7 Aligning the text and specifying a width
  • 15.8 +f -f
  • 15.9 b o x
  • 15.10 Using , as a thousand seperator
  • 15.11 More==>Refer to doc-pdf(Python 参考手册)-library.pdf–>String services.

1 %

>>> '%-*s' % (10, 'hello')
'hello     '
>>> '%*s' % (10, 'hello')
'     hello'
- 代表左对齐
*后面括号中有数字，代表长度  

2 不言而喻

append()
len()

3 find()

find(sub[, start[, end]]) 返回最先找到的sub的索引，若查找失败则返回-1

4 replace()

S.replace(old, new [, count]) -> string

5 split() rsplit()

str.split([sep [,maxsplit]]) -> list of strings

>>> line = '1,2,3,4,5,6'
>>> line.split(',')
['1', '2', '3', '4', '5', '6']
>>> line.split(',', 4)
['1', '2', '3', '4', '5,6']
>>> line.rsplit(',', 4)
['1,2', '3', '4', '5', '6']

6 strip rstrip lstrip

str.strip() #Return a copy of the string S with leading and trailing whitespace removed.
rstrip() #Return a copy of the string S with trailing whitespace removed.
lstrip() #Return a copy of the string S with leading whitespace removed.

7 center() ljust() rjust()

center(...)
    S.center(width[, fillchar]) -> str

>>> s.ljust(10, 'x')
'1.2xxxxxxx'
>>> s.rjust(10, 'x')
'xxxxxxx1.2'
>>> s.center(10, 'x')
'xxx1.2xxxx'

8 partition() rpartition()

rpartition(...)
    S.rpartition(sep) -> (head, sep, tail)
    
    Search for the separator sep in S, starting at the end of S, and return
    the part before it, the separator itself, and the part after it.  If the
    separator is not found, return two empty strings and S.

>>> str = 'hello world'
>>> str.rpartition(' ') 
('hello', ' ', 'world')
>>> str.partition(' ')
('hello', ' ', 'world')
>>> str.rpartition('l')  #只分一次
('hello wor', 'l', 'd')
>>> str.partition('l') #返回tuple，并且显示分隔的sep
('he', 'l', 'lo world')
>>> str.split(' ') #返回 list
['hello', 'world']

9 isdigit() isnumeric()

好像没有什么区别？

isdigit(...)
    S.isdigit() -> bool
    
    Return True if all characters in S are digits
    and there is at least one character in S, False otherwise
isnumeric(...)
    S.isnumeric() -> bool
    
    Return True if there are only numeric characters in S,
    False otherwise.
    

10 swapcase()

#返回大小写相互转化的结果
>>> line = 'HellO WOrld'
>>> line.swapcase()
'hELLo woRLD'

11 zfill()

#字符串左边填充0
>>> line.zfill(15)
'0000HellO WOrld'   

12 expandtabs()

S.expandtabs([tabsize]) -> str
The default tabsize is 8.
>>> line
'a\tb\tc'
>>> line.expandtabs()
'a       b       c'

13 isalpha isdigit isalnum islower isspace istitle isupper istitle title capitalize

并没有iscapitalize函数，不过可以自己实现：

def iscapitalize(s):
   return s == s.capitalize()

>>> a = 'hello world'
>>> a.capitalize()
'Hello world'
>>> a.title()
'Hello World'
>>> a  = 'Hello world'
>>> a.istitle()
False
>>> a  = 'Hello World'
>>> a.istitle()
True

14 maketrans translate

3.X中实现：

>>> map = str.maketrans('he', 'sh')
>>> str.translate(map)
'shllo world'
>>> str
'hello world'

2.X中下面的方法可靠，但在3.X中不行

string.maketrans(from, to) #from to must have the same length.
string.translate(s, table[, deletechars])
str.translate(table[, deletechars])
unicode.translate(table)

>>> import string
>>> map = string.maketrans('123', 'abc')
>>> s = '2341321234232123'
>>> s.translate(map)
'bc4acbabc4bcbabc'

import string 
def translator(frm='', to='', delete='', keep=None): 
if len(to) == 1: 
        to = to * len(frm) 
    trans = string.maketrans(frm, to) 
    if keep is not None: 
        allchars = string.maketrans('', '') 
        delete = allchars.translate(allchars, keep.translate(allchars,delete))
    def translate(s): 
        return s.translate(trans, delete) 
    return translate

15 format()

15.1 基本格式

{fieldname ! conversionflag : formatspec}
fieldname: number(a potitional argument) or keyword(named keyword argument)
                   .name or [index]
                   "Weight in tons {0.weight}"
                   "Units destroyed: {players[1]}"
conversionflag: s r a ==>str repr ascii
formatspec: [[fill]align[sign] [#] [0] [width] [.percision] [typecode]]
                     fill ==> 除{} 外的所有字符都可以
                     align==>    > < = ^
                     sign ==> '+' '-' ' '
                                      '-' 为默认情况 正数不显示＋负数显示－
                                      '+'表正负数都显示符号
                                      'space' 表示数字前面显示一空格
                     width precision ==> integer
                     type ==>  b c d e E f F g G n o   

15.2 Accessing arguments by potition:

>>> print '{0} {1} {2}'.format('a', 'b', 'c')
a b c
>>> '{2}, {1}, {0}'.format(*'abc')   ### *
'c, b, a'

>>> 'My {1[spam]} runs {0.platform}'.format(sys, {'spam': 'laptop'})
'My laptop runs linux2'

15.3 Accessing arguments by name:

>>> 'Coordinates: {latitude}, {longtitude}'.format(latitude = '23.2N', longtitude = '-112.32W')
'Coordinates: 23.2N, -112.32W'

>>> coord = {'latitude': '23.12N', 'longtitude': '-23.23W'}
>>> 'Coordinates: {latitude}, {longtitude}'.format(**coord)
'Coordinates: 23.12N, -23.23W'

>>> print '{name} {age}'.format(age=12, name='admin')
admin 12

>>> 'My {config[spam]} runs {sys.platform}'.format(sys=sys, config={'spam': 'laptop'})
'My laptop runs linux2'

15.4 Accessing arguments' attributes:

>>> c = 3 -5j
>>> 'The complex number {0} is formed from the real part {0.real} and the imaginary part {0.imag}'.format(c)
'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0'

15.5 Accessing argument's items:

>>> coord = (3, 5)
>>> 'X: {0[0]}; Y: 0[1]'.format(coord)
'X: 3; Y: 0[1]'
>>> print '{array[2]}'.format(array=range(10))
2

15.6 !s !r

>>> "repr() show quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2')
"repr() show quotes: 'test1'; str() doesn't: test2"

15.7 Aligning the text and specifying a width

>>> '{: <30}'.format('left aligned')
'left aligned                  '
>>> '{: >30}'.format('right aligned')
'                 right aligned'
>>> '{: ^30}'.format('centered')
'           centered           '
>>> '{:*^30}'.format('centered')
'***********centered***********'

15.8 +f -f

>>> '{:-f}; {:-f}'.format(3.14, -3.14)
'3.140000; -3.140000'
>>> '{:+f}; {:+f}'.format(3.14, -3.14) 
'+3.140000; -3.140000'
>>> '{:f}; {:f}'.format(3.14, -3.14)
'3.140000; -3.140000'

15.9 b o x

>>> 'int: {0: d}; hex: {0: x}; oct: {0: o}; bin{0: b}'.format(42)
'int:  42; hex:  2a; oct:  52; bin 101010'
# # with 0x, 0o, or 0b as prefix:
>>> 'int: {0: d}; hex: {0: #x}; oct: {0: #o}; bin{0: #b}'.format(42)
'int:  42; hex:  0x2a; oct:  0o52; bin 0b101010'

15.10 Using , as a thousand seperator

>>> '{: ,}'.format(12345678)
' 12,345,678'

15.11 More==>Refer to doc-pdf(Python 参考手册)-library.pdf–>String services.

>>> print '{attr.__class__}'.format(attr=0)
<type 'int'>

Author: visaya <visayafan@gmail.com>

Date: 2011-08-01 19:12:35 CST

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