Python detailing regular expressions (explaining commonly used key characters)

Official website

module RE
{
The RE module provides an interface to the regular expression engine that allows you to compile restring on objects and use them for matching
}
Question: The string before the function of R, the backslash will not be any special processing
{
Compile Flag-flages
Dotall[s] to match all characters including line breaks
Ignorecase[i] To make the match case insensitive
LOCALE[L], do localization identification (locale-aware) match French, etc.
Multiline[m], multiline match, impact ^ and $
VARBOSE[X], the ability to use the verbose state of RES to make it easier to understand
}

1.[...] Used to represent a set of characters, listed separately: [IO] matches ' i ', or ' o '

import res=‘tip top‘r=r‘t[io]p‘a=re.findall(r,s)print a

[...] If the match is a range, this write [0-9a-za-b] can represent 0 to 9 and a to Z and a to B

2.^⑴ characters not in []: [^io] matches characters other than i,o

import res=‘tip top‘r=r‘t[^io]p‘a=re.findall(r,s)print a

⑵ matches the beginning of a string

    import re    s=‘ahello hello‘    r=r‘^hello‘    a=re.findall(r,s)    print a

3.$ matches the following string

import res=‘hello hello‘r=r‘hello$‘a=re.findall(r,s)print a

4.[...^ ...]"Besides writing at the beginning of the place"and [.. or [ ...] or [... $] this has no effect and will only be treated as a generic character.

5. If the match string ^abc, there will be a problem, because ^ is a special character

import res=‘^abc ^abc ^abc‘r=r‘^abc‘a=re.findall(r,s)print a

The above problem can be resolved by an escape character

import res=‘^abc ^abc ^abc‘r=r‘\^abc‘a=re.findall(r,s)print a

3.9
-The backslash arrangement can add different character utilises to express different special meanings
-can also be used to get out of the sludge without dyeing all the meta-characters: [or \
⑴\d matches any decimal number, which is equivalent to class [0-9]
⑵\D matches any non-numeric character, which is equivalent to class [^0-9]
⑶\s matches any whitespace character, which is equivalent to class [\t\n\r\f\v]
⑷\w matches any alphanumeric character, which is equivalent to a class [a-za-z0-9]
⑸\w matches any non-alphanumeric character, which is equivalent to class [^a-za-z0-9]

7. Duplicate questions
If you match a phone number, for the number, you re-use \d is very troublesome, how to solve

import ren=‘18829789854‘r=r‘^1\d\d\d\d\d\d\d\d\d\d‘print re.findall(r,n)

Workaround: Use {Number},number to indicate the number of repetitions

import ren=‘18829789854‘r=r‘^1\d{10}$‘   #对于电话号码前面和后面不能现出现别的字符，所以使用^和$   print re.findall(r,n)   

8.* specifies that the previous character can be matched 0 or more times instead of only once. Match engine tries to repeat as many times as I can (no more than integer office range, 2 billion)

import urllib,reh=urllib.urlopen(‘http://www.baidu.com‘)s=h.read()r=‘www.\w*.com‘  #两个.之间想匹配多个字母或数字li=re.findall(r,s)forin li:    print i

9.+ the difference between this and * is that at least once, that is, match the preceding character (the number of times >=1), all for the URL match, you should use the + sign

import urllib,reh=urllib.urlopen(‘http://www.baidu.com‘)s=h.read()r=‘www.\w+.com‘  #两个.之间不会出现0次li=re.findall(r,s)forin li:    print i

10.? ⑴ indicates that the preceding symbol repeats once or 0 times
⑵ represents the minimum number of matches, if you want to get the shortest match of AB

import res=‘abbbbbbb‘r=r‘ab+‘print re.findall(r,s)       

Shortest:

import res=‘abbbbbbb‘r=r‘ab+?‘print re.findall(r,s)       

There is also a role:

import rer=r‘(?:\d{1}){2}‘       #让组里面的内容连着再次s=‘fas14214jiojoi2412‘str_re=re.compile(r)print str_re.findall(s)

11. Use {M,n} if you want to match the previous symbol to a certain range

import res=‘abbbb‘r=r‘ab{1,3}‘        #表示b的次数出现1次到3次，包括1和3print re.findall(r,s)       

12. If your regular expression, repeated use of the pre-compilation, so as to improve the efficiency of operation, the code is as follows

import rer=re.compile(r‘ab‘#把正则表达式提前编译好print r.findall(字符串)

13. If the match, if you want to match the case, you can compile it.

• Re.compile (regular expression, re. I) #re. I means ignoring case

14. Methods

• Match () determines whether the re matches the starting position of the string
• Search () scan string to find the first position of this re match #前两个返回的是一个对象, if you want to see the results

import res=‘ aab‘r=re.compile(r‘ab‘)t=r.search(s)print t.group()

Goups () group

import rer=r‘(\d)\w*(\d)‘s=‘fas14214jiojoi2412‘str_re=re.compile(r)str_object=str_re.search(s)print str_object.groups()  #以元组输出分组的结果

• FindAll () finds all the substrings that the re matches and returns them as a list
• Finditer () finds all the substrings that the re matches and returns them as an iterator #返回一个迭代器对象

15.MatchObject (Match object)

• Group () returns a string that is matched by re
• Start () returns the position where the match started
• End () returns the position of the end of the match
• Span () returns a tuple containing the position of the match (start, end)

16. What if you want to replace a string that matches a regular expression?

import res=‘ aab‘r=re.compile(r‘ab‘)t=r.sub(‘AB‘,s)   #‘AB‘是把符合正则表达式的字符换掉print t

There is also a function, SUBN () returns a string, and returns the number of changes

17. Want to split the content that matches the regular expression

import res=‘ 1+2-3*4/5‘r=re.compile(r‘[\+\-\*/]‘)   #因为+-*都是特殊字符所有要加上\t=r.split(s)print

. (dot) matches any character, except the newline character, when re. When the Dotall tag is specified, it can match any character that includes a line feed.

19. If a match is encountered, it will not be considered an escape character when it encounters \ n and other escape characters, all at compile time.
Re.compile (regular expression, re. S

import rer=re.compile(r‘.net‘,re.S)print r.findall(‘\nnet‘)        

19. If you are dealing with multiple lines of string, you can use it to re. M, for example: for file processing

import res=‘‘‘ababcabcd‘‘‘r=re.compile(r‘^a‘,re.M)print r.findall(s)  

18. For regular expressions, when writing on multiple lines, use re. X

import rern=r‘‘‘a‘‘‘s=‘a‘r=re.compile(rn,re.X)print r.findall(s)

19. Grouping, selecting for string fragments, using (... | ... | ....)
Example 1:

import res=‘www.baidu.cn‘r=re.compile(r‘www\.\w+\.(com|cn)‘,re.X)print r.match(s)    

If you use FindAll () to match, the following behavior occurs

import res=‘www.baidu.cn‘r=re.compile(r‘www\.\w+\.(com|cn)‘,re.X)print r.findall(s)

Results:
[' CN ']

Returns the contents of a group

Example 2:

import res=‘name=1 name=2‘r=re.compile(r‘name=(\d)‘,re.X)print r.findall(s)

Results:
[' 1 ', ' 2 ']

Only get the contents of the grouping, if there is no grouping symbol, it also returns the Name= etc.

Python detailing regular expressions (explaining commonly used key characters)