Python 中正则表达式的使用浅析

Python 学习，请参考这个网站：
https://pythonprogramming.net/
很多专题，每个都有视频，我觉得讲得不错。

Python 中的 正则表达式 （Regular Expression）的模块是： re

正则表达式中常见的各种rule:

Identifiers:

\d = any number
\D = anything but a number
\s = space
\S = anything but a space
\w = any letter
\W = anything but a letter
. = any character, except for a new line
\b = space around whole words
\. = period. must use backslash, because . normally means any character.

Modifiers:

{1,3} = for digits, u expect 1-3 counts of digits, or "places" 
+ = match 1 or more
? = match 0 or 1 repetitions.
* = match 0 or MORE repetitions
$ = matches at the end of string
^ = matches start of a string
| = matches either/or. Example x|y = will match either x or y
[] = range, or "variance"
{x} = expect to see this amount of the preceding code.
{x,y} = expect to see this x-y amounts of the precedng code

White Space Charts:

\n = new line
\s = space
\t = tab
\e = escape
\f = form feed
\r = carriage return

Characters to REMEMBER TO ESCAPE IF USED!

. + * ? [ ] $ ^ ( ) { } | \

Brackets:

[] = quant[ia]tative = will find either quantitative, or quantatative.
[a-z] = return any lowercase letter a-z
[1-5a-qA-Z] = return all numbers 1-5, lowercase letters a-q and uppercase A-Z

举例说明：

import re

exampleString = '''
Jessica is 15 years old, and Daniel is 27 years old.
Edward is 97 years old, and his grandfather, Oscar, is 102.
'''

ages = re.findall(r'\d{1,3}', exampleString)
names = re.findall(r'[A-Z][a-z]*', exampleString)

print(ages)
#print is:['15', '27', '97', '102']
print(names)
#print is:['Jessica', 'Daniel', 'Edward', 'Oscar']

ageDict={}
x=0
for eachName in names:
ageDict[eachNmae] = ages[x]
x+=1

print(ageDict)
#print is: {'Jessica': '15', 'Oscar': '102', 'Edward': '97', 'Daniel': '27'}



上面的例子中只用到了re.findall () 这一个函数，re模块还有很多其他的函数。

re.findall() 返回的是 列表。

举例2：

用到了re.sub() 函数。

re.sub()  用来实现通过正则表达式，实现比普通字符串的replace更加强大的替换功能；

如果输入字符串是：

而你是想把123和456，都换成222

就需要借助于re.sub，通过正则表达式，来实现这种相对复杂的字符串的替换：

当然，实际情况中，会有比这个例子更加复杂的，其他各种特殊情况，就只能通过此re.sub去实现如此复杂的替换的功能了。

所以，re.sub的功能就是：

对于输入的一个字符串，利用正则表达式（的强大的字符串处理功能），去实现（相对复杂的）字符串替换处理，然后返回被替换后的字符串

其中re.sub还支持各种参数，比如count指定要替换的个数等等。