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

#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

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.

Regular matching

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))

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• 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))

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• 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))

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• 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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