Python基础教程之第3章 使用字符串

Posted 2020-09-22

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' % 1,1,2

Traceback (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
'!"#$%&\'()*+,-./:;<=>?
@[\\]^_`{|}~'
>>> string.printable
'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\'()*+,-./:;<=>[email protected][\\]^_`{|}~ \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 '=' * width

print header_format % (item_width, 'Item', price_width, 'Price')

print '-' * width

print 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
#===================================