How to implement overlapping matching with python regular expressions

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Regular expressions to implement overlapping matching

import regex
string = '100101010001'
str_re = '101'
print(regex.findall(str_re, string, overlapped=True))

Ordinary re library matching can only match one '101'.

Regular expression and regular matching

Regular expression

Regular expression can be understood as an expression for filtering data, which is a limited number of atoms and metacharacters.

Atoms: Basic unit, each expression has at least one atom

Ordinary characters make up atoms
Non-printing characters make up atoms (Characters that are not printed on the output station)	\n ：Line break \t：Tab backspace character
Common characters form atoms	\w: Match any letter, Numbers, underscores \W: Opposite of \w \d: Matches any decimal number \D: Opposite of \d \s : Matches any whitespace characters, such as spaces, newlines, indents \S: Opposite of \s
Atomic table composed of atoms	A group of atoms forms a table, which is declared by [] The priorities of the atoms in the table are equal, but the contents only appear in order If the atom table starts with ^, it means inversion

#普通字符组成原子
pat1 = "abcd"
 
#非打印字符组成原子
pat2 = "\n"
 
#通用字符做原子
pat3 = "\w"
 
#原子表组成原子
pat4 = "py[abc]"
#可以匹配pya，pyb，pyc，但匹配pyab等原子表重复出现的情况失败
 
#原子表开头带 ^ 表示取反
pat5 = "py[^abc]"
#第三个位置匹配除了a，b，c外的任意一个字符

Metacharacters: Characters with special meaning in regular expressions

.	Matches any character, except newline characters
^	Matches the beginning of the string
$	Matches the end position of the string. When there are multiple sets of matching matches, the last set of matches in the string is returned.
*	Match 0, 1, n times the previous atom [Greedy mode: match as many as possible]
?	Match 0, 1 time the previous atom [Lazy mode: exact match]
	Match 1, n times the previous atom
{ j }	The preceding atom appears j times
{ j , }	The preceding atom appears at least j times
{ j , k }	The preceding atom appears at least j times and at most k times
i | j	matches i or j, if i and j appear at the same time, matching the i
( )	group, restricting the combination of this group of data to be as described in (), and only returning the description in brackets The content

Pattern modifier

is the parameter at the flag position in the function, which can be changed without changing the regular expression. Its meaning is to adjust the matching results.

##re.S matches including newline characters

re.I	Ignore case when matching
re.M	Multi-line matching
re.L	Localized identification matching
re.U	according to Unicon character matching, affecting \w \W

Regular matching

Regular expressions perform fuzzy matching on strings, and one application is regular matching. Regular matching is a technology used by python crawlers to extract target information from crawled text information.

Commonly used functions for regular matching: (call the regular expression module re)

• re.search(pat, str[, flag]) : Scan the string str and return the position of pat (the first successful match). Flag is used to control the matching method of regular expressions

import re
str = 'python'
pat = 'pytho[a-n]'
print(re.search(pat, str))

• re. match(pat, str[, flag]): Scan the starting position of the string str and return the position of pat (the first successful match). Flag is used to control the matching method of the regular expression [if it starts, it will not If it matches, it ends and returns none】

import re
str_1 = 'hello world'
str_2 = 'world hello'
pat = 'world'
print(re.match(pat, str_1))
print(re.match(pat, str_2))

• re.complie(pat[, flag]): Compile the regular expression pat and return the regular expression object
• findall(str[, pos[, endpos]]): Match all, use a list to return all matched substrings in string [not just the first time], pos and endpos can be specified in Starting position in string
• re.complie(pat).findall(str): Global matching function, matches all substrings in str that match pat, loads a list and returns the result

import re
str = "hello world hello world hello world"
pat = "hello"
print(re.complie(pat).findall(str))
print(re.complie(pat).findall(str, 5, 15))

• re.sub(pat, repl, str[, count[, flag]]): Replace matching items in the string [clean data], You can use count to specify the maximum number of replacements

import re
str = "400-823-823"
pat = "-"
#短横改空格，最大替换次数2
str_new = re.sub(pat, " ", str, count=2)

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