两天研习Python基础（九）文本处理

字符串方法

转换字符
- str.maketrans()获取转换表
- translate()基于转换表执行字符串映射
maketrans()第一个参数是被取代的字符，第二个参数是取代的字符，第三个是被映射为None的字符
字符转换例子[1]

代码语言：javascript复制

>>> greeting = '===== Have a great day ====='
>>> greeting.translate(str.maketrans('=', '-'))
'----- Have a great day -----'

>>> greeting = '===== Have a great day!! ====='
>>> greeting.translate(str.maketrans('=', '-', '!'))
'----- Have a great day -----'

>>> import string
>>> quote = 'SIMPLICITY IS THE ULTIMATE SOPHISTICATION'
>>> tr_table = str.maketrans(string.ascii_uppercase, string.ascii_lowercase)
>>> quote.translate(tr_table)
'simplicity is the ultimate sophistication'

>>> sentence = "Thi1s is34 a senten6ce"
>>> sentence.translate(str.maketrans('', '', string.digits))
'This is a sentence'
>>> greeting.translate(str.maketrans('', '', string.punctuation))
' Have a great day '

移除首/尾/两者的字符串
仅移除首/尾连续的字符
默认空格会被除去
如果指定了多个字符，它会被视为集合，并使用其中所有的组合

代码语言：javascript复制

>>> greeting = '      Have a nice day :)     '
>>> greeting.strip()
'Have a nice day :)'
>>> greeting.rstrip()
'      Have a nice day :)'
>>> greeting.lstrip()
'Have a nice day :)     '

>>> greeting.strip(') :')
'Have a nice day'

>>> greeting = '===== Have a great day!! ====='
>>> greeting.strip('=')
' Have a great day!! '

风格化
width参数指定了总的输出字符串长度

代码语言：javascript复制

>>> ' Hello World '.center(40, '*')
'************* Hello World **************'

改变大小写和大小写检查

代码语言：javascript复制

>>> sentence = 'thIs iS a saMple StrIng'

>>> sentence.capitalize()
'This is a sample string'

>>> sentence.title()
'This Is A Sample String'

>>> sentence.lower()
'this is a sample string'

>>> sentence.upper()
'THIS IS A SAMPLE STRING'

>>> sentence.swapcase()
'THiS Is A SAmPLE sTRiNG'

>>> 'good'.islower()
True

>>> 'good'.isupper()
False

检查是否字符串由数值构成

代码语言：javascript复制

>>> '1'.isnumeric()
True
>>> 'abc1'.isnumeric()
False
>>> '1.2'.isnumeric()
False

检查是否字符串序列是否存在

代码语言：javascript复制

>>> sentence = 'This is a sample string'
>>> 'is' in sentence
True
>>> 'this' in sentence
False
>>> 'This' in sentence
True
>>> 'this' in sentence.lower()
True
>>> 'is a' in sentence
True
>>> 'test' not in sentence
True

获取字符序列存在的次数（非覆盖）

代码语言：javascript复制

>>> sentence = 'This is a sample string'
>>> sentence.count('is')
2
>>> sentence.count('w')
0

>>> word = 'phototonic'
>>> word.count('oto')
1

匹配头尾字符序列

代码语言：javascript复制

>>> sentence
'This is a sample string'

>>> sentence.startswith('This')
True
>>> sentence.startswith('The')
False

>>> sentence.endswith('ing')
True
>>> sentence.endswith('ly')
False

基于字符序列分割字符串
返回列表
要使用正则表达式分割，使用re.split()

代码语言：javascript复制

>>> sentence = 'This is a sample string'

>>> sentence.split()
['This', 'is', 'a', 'sample', 'string']

>>> "oranges:5".split(':')
['oranges', '5']
>>> "oranges :: 5".split(' :: ')
['oranges', '5']

>>> "a e i o u".split(' ', maxsplit=1)
['a', 'e i o u']
>>> "a e i o u".split(' ', maxsplit=2)
['a', 'e', 'i o u']

>>> line = '{1.0 2.0 3.0}'
>>> nums = [float(s) for s in line.strip('{}').split()]
>>> nums
[1.0, 2.0, 3.0]

连接字符串列表

代码语言：javascript复制

>>> str_list
['This', 'is', 'a', 'sample', 'string']
>>> ' '.join(str_list)
'This is a sample string'
>>> '-'.join(str_list)
'This-is-a-sample-string'

>>> c = ' :: '
>>> c.join(str_list)
'This :: is :: a :: sample :: string'

替换字符
第三个参数指定使用多少次的替换
变量必须显式地重赋值

代码语言：javascript复制

>>> phrase = '2 be or not 2 be'
>>> phrase.replace('2', 'to')
'to be or not to be'

>>> phrase
'2 be or not 2 be'

>>> phrase.replace('2', 'to', 1)
'to be or not 2 be'

>>> phrase = phrase.replace('2', 'to')
>>> phrase
'to be or not to be'

进一步阅读

Python文档 - 字符串方法[2]
python字符串方法教程[3]

正则表达式

正则表达式元素便利参考

元字符	描述
^	锚定，匹配字符串行首
$	锚定，匹配字符串行尾
.	匹配除换行符n之外的字符
\|	或操作符，用于匹配多个模式
()	用于模式分组和提取
[]	字符类 - 匹配多个字符中的一个
^	使用匹配元字符

量词	描述
*	匹配之前的字符0或多次
	匹配之前的字符1或多次
?	匹配之前的字符0或1次
{n}	匹配n次
{n,}	匹配至少n次
{n,m}	匹配至少n次，至多m次

字符类	描述
[aeiou]	匹配任何元音
[^aeiou]	^ 倒置选择，所以这会匹配任何的辅音
[a-f]	匹配abcdef中任意字符
d	匹配数字，跟[0-9]一样
D	匹配非数字，跟 [^0-9] 或 [^d]一样
w	匹配字母和下划线，跟[a-zA-Z_]一样
W	匹配非字母和非下划线字符，跟[^a-zA-Z_] 或 [^w]一样
s	匹配空格符，跟[ tnrfv]一样
S	匹配非空行符，跟[^s]一样
b	单词边界，单词定义为字母序列
B	非单词边界

编译标记	描述
re.I	忽略大小写
re.M	多行模式，^和 $ 锚定符号可以处理中间行
re.S	单行模式，.也会匹配n
re.V	冗余模式，提高可读性和添加注释

Python文档 - 标记[4] - 详情和标记长名

变量	描述
1, 2, 3 等等	引用匹配的模式
g<1>, g<2>, g<3> etc	引用匹配的模式，用于区分数字和引用

模式匹配和提取

匹配/提取字符序列
使用re.search()查看是否一个字符串包含某个模式
使用re.findall()获得一个匹配模式列表
使用re.split()获得一个基于模式分割字符串的列表
它们的语法如下

代码语言：javascript复制

re.search(pattern, string, flags=0)
re.findall(pattern, string, flags=0)
re.split(pattern, string, maxsplit=0, flags=0)

代码语言：javascript复制

>>> import re
>>> string = "This is a sample string"

>>> bool(re.search('is', string))
True

>>> bool(re.search('this', string))
False

>>> bool(re.search('this', string, re.I))
True

>>> bool(re.search('T', string))
True

>>> bool(re.search('is a', string))
True

>>> re.findall('i', string)
['i', 'i', 'i']

使用正则表达式
当使用正则表达式元素时用r''格式

代码语言：javascript复制

>>> string
'This is a sample string'

>>> re.findall('is', string)
['is', 'is']

>>> re.findall('bis', string)
[]

>>> re.findall(r'bis', string)
['is']

>>> re.findall(r'w ', string)
['This', 'is', 'a', 'sample', 'string']

>>> re.split(r's ', string)
['This', 'is', 'a', 'sample', 'string']

>>> re.split(r'd ', 'Sample123string54with908numbers')
['Sample', 'string', 'with', 'numbers']

>>> re.split(r'(d )', 'Sample123string54with908numbers')
['Sample', '123', 'string', '54', 'with', '908', 'numbers']

引用

代码语言：javascript复制

>>> quote = "So many books, so little time"

>>> re.search(r'([a-z]{2,}).*1', quote, re.I)
<_sre.SRE_Match object; span=(0, 17), match='So many books, so'>

>>> re.search(r'([a-z])1', quote, re.I)
<_sre.SRE_Match object; span=(9, 11), match='oo'>

>>> re.findall(r'([a-z])1', quote, re.I)
['o', 't']

搜索和替换

语法

代码语言：javascript复制

re.sub(pattern, repl, string, count=0, flags=0)

简单替换
re.sub不会改变传入变量的值，必须显式地指定

代码语言：javascript复制

>>> sentence = 'This is a sample string'
>>> re.sub('sample', 'test', sentence)
'This is a test string'

>>> sentence
'This is a sample string'
>>> sentence = re.sub('sample', 'test', sentence)
>>> sentence
'This is a test string'

>>> re.sub('/', '-', '25/06/2016')
'25-06-2016'
>>> re.sub('/', '-', '25/06/2016', count=1)
'25-06/2016'

>>> greeting = '***** Have a great day *****'
>>> re.sub('*', '=', greeting)
'===== Have a great day ====='

引用

代码语言：javascript复制

>>> words = 'night and day'
>>> re.sub(r'(w )( w  )(w )', r'321', words)
'day and night'

>>> line = 'Can you spot the the mistakes? I i seem to not'
>>> re.sub(r'b(w ) 1b', r'1', line, flags=re.I)
'Can you spot the mistakes? I seem to not'

在re.sub()替换部分使用函数

代码语言：javascript复制

>>> import math
>>> numbers = '1 2 3 4 5'

>>> def fact_num(n):
...     return str(math.factorial(int(n.group(1))))
...
>>> re.sub(r'(d )', fact_num, numbers)
'1 2 6 24 120'

>>> re.sub(r'(d )', lambda m: str(math.factorial(int(m.group(1)))), numbers)
'1 2 6 24 120'

从re.sub调用函数[5]
用函数输出替换字符串模式[6]
lambda教程[7]

编译正则表达式

代码语言：javascript复制

>>> swap_words = re.compile(r'(w )( w  )(w )')
>>> swap_words
re.compile('(\w )( \w  )(\w )')

>>> words = 'night and day'

>>> swap_words.search(words).group()
'night and day'
>>> swap_words.search(words).group(1)
'night'
>>> swap_words.search(words).group(2)
' and '
>>> swap_words.search(words).group(3)
'day'
>>> swap_words.search(words).group(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: no such group

>>> bool(swap_words.search(words))
True
>>> swap_words.findall(words)
[('night', ' and ', 'day')]

>>> swap_words.sub(r'321', words)
'day and night'
>>> swap_words.sub(r'321', 'yin and yang')
'yang and yin'

正则表达式进一步阅读

Python文档 - re模块[8]
Python文档 - 正则表达式使用介绍[9]
developers.google - 正则表达式教程[10]
automatetheboringstuff - 正则表达式[11]
综合参考：regex是什么？[12]
练习工具
- online regex tester[13] 展示解释，提供参考指南和保存、分享regex
- regexone[14] - 交互式教程
- cheatsheet[15] - 交互式[16]学习
- regexcrossword[17] - 通过解答纵横游戏练习，开始之前阅读'How to play'部分

参考资料

[1]

字符转换例子: https://stackoverflow.com/questions/555705/character-translation-using-python-like-the-tr-command

[2]

Python文档 - 字符串方法: https://docs.python.org/3/library/stdtypes.html#string-methods

[3]

python字符串方法教程: http://www.thehelloworldprogram.com/python/python-string-methods/

[4]

Python文档 - 标记: https://docs.python.org/3/howto/regex.html#compilation-flags

[5]

从re.sub调用函数: https://stackoverflow.com/questions/11944978/call-functions-from-re-sub

[6]

用函数输出替换字符串模式: https://stackoverflow.com/questions/12597370/python-replace-string-pattern-with-output-of-function

[7]

lambda教程: https://pythonconquerstheuniverse.wordpress.com/2011/08/29/lambda_tutorial/

[8]

Python文档 - re模块: https://docs.python.org/3/library/re.html

[9]

Python文档 - 正则表达式使用介绍: https://docs.python.org/3/howto/regex.html

[10]

developers.google - 正则表达式教程: https://developers.google.com/edu/python/regular-expressions

[11]

automatetheboringstuff - 正则表达式: https://automatetheboringstuff.com/chapter7/

[12]

综合参考：regex是什么？: https://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean

[13]

online regex tester: https://regex101.com/#python

[14]

regexone: http://regexone.com/

[15]

cheatsheet: https://www.shortcutfoo.com/app/dojos/python-regex/cheatsheet

[16]

交互式: https://www.shortcutfoo.com/app/dojos/python-regex

[17]

regexcrossword: https://regexcrossword.com/

https 网络安全正则表达式 regex

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两天研习Python基础（九） 文本处理

字符串方法

正则表达式

模式匹配和提取

搜索和替换

编译正则表达式

正则表达式进一步阅读

参考资料

两天研习Python基础（九）文本处理