Python基础教程之第3章 使用字符串

Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)] on win32
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#3.1基本字符串操作
>>> website = 'http://www.python.org'
>>> website[-3:]='com'Traceback (most recent call last):File "<pyshell#1>", line 1, in <module>website[-3:]='com'
TypeError: 'str' object does not support item assignment
#3.2 字符串格式化:精简版
>>> format = "Hello, %s. %s is enough for ya?"
>>> values = ('world', 'Hot')
>>> print format % values
Hello, world. Hot is enough for ya?
>>> format = "Pi with three decimals: %.3f"
>>> from math import pi
>>> print format % pi
Pi with three decimals: 3.142
#模板字符串
>>> from string import Template
>>> s = Template('$x, glorious $x!')
>>> s.substitute(x='slurm')
'slurm, glorious slurm!'
>>> s = Template("It's ${x}tastic!")
>>> s.substitute(x='slurm')
"It's slurmtastic!"
>>> s = Template("Make $$ selling $x!")
>>> s.substitute(x='slurm')
'Make $ selling slurm!'
>>> s = Template('A $thing must never $action.')
>>> d={}
>>> d['thing']='gentleman'
>>> d['action']='show his socks'
>>> s.substitute(d)
'A gentleman must never show his socks.'
>>> #saft_substitute不会因缺少值或不对使用$字符而出错.
>>> '%s plus %s equlas %s' % (1,1,2)
'1 plus 1 equlas 2'
>>> '%s plus %s equlas %s' % 1,1,2Traceback (most recent call last):File "<pyshell#24>", line 1, in <module>'%s plus %s equlas %s' % 1,1,2
TypeError: not enough arguments for format string
>>> '%s plus %s equlas %s' % 1,1,2 # Lacks parentheses!Traceback (most recent call last):File "<pyshell#25>", line 1, in <module>'%s plus %s equlas %s' % 1,1,2 # Lacks parentheses!
TypeError: not enough arguments for format string
#3.3 字符串格式化:完整版
#3.3.1简单转换
>>> 'Price of eggs: $%d' % 42
'Price of eggs: $42'
>>> 'Hexadecimal price of eggs: %x' % 42
'Hexadecimal price of eggs: 2a'
>>> from math import pi
>>> 'Pi: %f...' % pi
'Pi: 3.141593...'
>>> 'Very inexact estimate of pi: %i' % pi
'Very inexact estimate of pi: 3'
>>> 'Using str: %s' % 42L
'Using str: 42'
>>> 'Using repr: %r' % 42L
'Using repr: 42L'
#3.3.2字段宽度和精度
>>> '%10f' % pi
'  3.141593'
>>> '%10.2f' % pi
'      3.14'
>>> '%.2f' % pi
'3.14'
>>> '%.5s' % 'Guido van Rossum'
'Guido'
>>> '%.*s' % (5, 'Guido van Rossum')
'Guido'
#3.3.3符号, 对齐和0填充
>>> '%010.2f' % pi
'0000003.14'
>>> 010
8
>>> '%-10.2f' % pi
'3.14      '
>>> print ('% 5d' % 10) + '\n' + ('% 5d' % -10)F
SyntaxError: invalid syntax
>>> print ('% 5d' % 10) + '\n' + ('% 5d' % -10)10-10
>>> print ('% 5d' % 10) + '\n' + ('% 5d' % -10)F
SyntaxError: invalid syntax
>>> print ('% 5d' % 10) + '\n' + ('% 5d' % -10)10-10
>>> print ('%+5d' % 10) + '\n' + ('%+5d' % -10)+10-10#代码清单3-1 字符串格式化演示样例
#3.4字符串方法
#string模块还包含一些不能作为字符串方式使用的常量和函数
>>> import string
>>> string.digits
'0123456789'
>>> string.letters
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
>>> string.lowercase
'abcdefghijklmnopqrstuvwxyz'
>>> string.uppercase
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> string.punctuation
'!"#$%&\'()*+,-./:;<=>?

@[\\]^_`{|}~' >>> string.printable '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c' >>> string.ascii_letters 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ' #3.4.1 find >>> 'With a moo-moo here. and a moo-moo there'.find('moo') 7 >>> title = "Monty Python's Flying Circus" >>> title.find('Monty') 0 >>> title.find('Python') 6 >>> titie.find('Flying') Traceback (most recent call last): File "<pyshell#59>", line 1, in <module> titie.find('Flying') NameError: name 'titie' is not defined >>> title.find('Flying') 15 >>> title.find('Zirquss') -1 >>> subject = '$$$ Get rich now!!! $$$' >>> subject.find('$$$') 0 >>> subject.find('$$$', 1) 20 >>> subject.find('!!!') 16 >>> subject.find('!!!', 0, 16) -1 #3.4.2 join >>> seq = [1,2,3,4,5] >>> sep = '+' >>> sep.join(seq) Traceback (most recent call last): File "<pyshell#69>", line 1, in <module> sep.join(seq) TypeError: sequence item 0: expected string, int found >>> seq = ['1','2','3','4','5'] >>> sep.join(seq) '1+2+3+4+5' >>> dirs = '','usr','bin','env' >>> '/'.join(dirs) '/usr/bin/env' >>> print 'C:' + '\\'.join(dirs) C:\usr\bin\env #3.4.3 lower >>> 'Trondheim Hammer Dance'.lower() 'trondheim hammer dance' >>> if 'Gumby' in ['gumby','smith','jones']: print 'Found it!' >>> name='Gumby' >>> names=['gumby','smith','jones'] >>> if name.lower() in names: print 'Found it!' Found it! #标题转换 >>> "that's all folks".title() "That'S All Folks" >>> import string >>> string.capwords("that's all, folks") "That's All, Folks" #3.4.4 replace >>> 'This is a test'.replace('is','eez') 'Theez eez a test' #3.4.5 split >>> '1+2+3+4+5'.split('+') ['1', '2', '3', '4', '5'] >>> '/usr/bin/env'.split('/') ['', 'usr', 'bin', 'env'] >>> 'Using the default'.split() ['Using', 'the', 'default'] #3.4.6 strip 相当于Java 中的 String.trim() >>> ' internal whitespace is kept '.strip() 'internal whitespace is kept' >>> names = ['gumby','smith','jones'] >>> name = 'gumby' >>> if name in names: print 'Found it!' Found it! >>> '*** SPAM * for * everyone!!! ***'.strip(' *!') 'SPAM * for * everyone' #3.4.7 translate >>> from string import maketrans >>> table = maketrans('cs', 'kz') >>> len(table) 256 >>> table[97:123] 'abkdefghijklmnopqrztuvwxyz' >>> maketrans('','')[97:123] 'abcdefghijklmnopqrstuvwxyz' >>> table = maketrans('cs','kz') >>> 'this is an incredible test'.translate(table) 'thiz iz an inkredible tezt' >>> 'this is an incredible test'.translate(table,' ') 'thizizaninkredibletezt' #非英语字符串问题 table = maketrans('X','x') word = 'Xxx' print word.translate(table).lower() print u'Xxx'.lower() #小结 #本章介绍了字符串的两种很重要的使用方式 #字符串格式化: 求模操作符(%)能够用来将其它值转换为包含转换标志的字符串,比如%s. 它还能用来对值进行不同方式的格式化, #包含左右对齐, 设定字段宽度以及精度,添加符号(正负号)或者左填充数字0等. #字符串方法 有些很实用,比方split和join,有些则用得很少,比方istitle或capitalize. #本章的新函数 #string.capwords(s[, sep]) 使用split函数切割字符串s(以sep为分隔符),使用capitalize函数将切割得到的各单词首字母大写,而且使用join函数以sep为分隔符 #将各单词连接起来 #string.maketrans(from,to) 创建用于转换的转换表 #接下来学什么 列表, 字符串和字典是Python中最重要的3种数据类型.

代码清单3-1 字符串格式化演示样例 

#e3-1
#使用给定的宽度打印格式化后的价格列表width = input('Plese enter width: ')price_width = 10
item_width = width - price_width;#减号(-1)用来左对齐数值
header_format = '%-*s%*s'
format = '%-*s%*.2f'print '=' * widthprint header_format % (item_width, 'Item', price_width, 'Price')print '-' * widthprint format % (item_width, 'Apples', price_width, 0.4)
print format % (item_width, 'Pears', price_width, 0.5)
print format % (item_width, 'Cantaloupes', price_width, 1.92)
print format % (item_width, 'Dried Apricots (16 oz.)', price_width, 8)
print format % (item_width, 'Prunes (4 lbs.)', price_width, 12)print '=' * width#python e3-1.py
#Plese enter width: 35
#===================================
#Item                          Price
#-----------------------------------
#Apples                         0.40
#Pears                          0.50
#Cantaloupes                    1.92
#Dried Apricots (16 oz.)        8.00
#Prunes (4 lbs.)               12.00
#===================================