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Summarize and organize python regular expression analysis

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This article brings you relevant knowledge about python, which mainly introduces issues related to Python regular expressions, and summarizes regular expression functions, metacharacters, special sequences, and sets. Sets, matching objects, etc. I hope this helps.

Summarize and organize python regular expression analysis

Recommended learning: python tutorial

What is the role of regular expressions? There is a lot of content captured by our web page, and we cannot get all of it. We only need part of it, so we need to use regular expressions to match the content we want.

Regular Expression Module

Python has a built-in package called re that can be used to handle regular expressions. Import the re module:

import re

Regular Expressions in Python

After importing the re module, you can start using regular expressions.
For example: Search a string to see if it starts with "The" and ends with "Spain":

import re

txt = "The rain in Spain"x = re.search("^The.*Spain$", txt)if x:
  print("匹配成功!")else:
  print("匹配失败")

Run:
Summarize and organize python regular expression analysis
Of course, you can't understand this right now For example, since we teach step by step, we will not teach you to reach the sky in one step.

Regular expression function

findall() function

The findall() function returns a list containing all matches.
Example: Print a list of all matches

import re

txt = "川川菜鸟啊菜鸟啊"x = re.findall("菜鸟", txt)print(x)

Running returns:
Summarize and organize python regular expression analysis
The list contains matches in the order they are found. If no match is found, an empty list is returned:

import re

txt = "菜鸟并不菜"x = re.findall("川川", txt)print(x)if (x):
  print("匹配成功了哟")else:
  print("找不到这个呀!")

Running returns:
Summarize and organize python regular expression analysis

##search() function

The search() function searches a string for a match and returns a Match object if there is a match. If there are multiple matches, only the

first occurrence of the match is returned. For example: Search for the first whitespace character in the string:

import re

txt = "菜鸟 呢"x = re.search("\s", txt)print("第一个空格字符位于位置:", x.start())
Running results:


Summarize and organize python regular expression analysis If no match is found, None returns this value:

import re

txt = "天上飞的是菜鸟"x = re.search("川川", txt)print(x)
Returns:


Summarize and organize python regular expression analysis

split() function

The split() function returns a list in which the string is split on each match.

For example: Split at each whitespace character

import re

txt = "菜鸟 学 python"x = re.split("\s", txt)print(x)
Running returns:


Summarize and organize python regular expression analysis You can control the number of occurrences by specifying the maxsplit parameter
For example: Only at the Split the string on one occurrence:

import re#Split the string at the first white-space character:txt = "飞起来 菜鸟 们"x = re.split("\s", txt, 1)print(x)
Returns:


Summarize and organize python regular expression analysis

sub() function

The sub() The function replaces matches with text of your choice.

For example: Run with only replacement

import re

txt = "学python就找川川菜鸟"x = re.sub("就", "只", txt)print(x)
:


Summarize and organize python regular expression analysis You can control the number of replacements by specifying the count parameter:
For example, replace the first 2 occurrences:

import re

txt = "学python就就就川川菜鸟"x = re.sub("就", "只", txt,2)print(x)
Returns:


Summarize and organize python regular expression analysis

Metacharacters

List symbols

[] Use On a set of characters For example: #Find all lowercase characters between "a" and "m" in alphabetical order

import re

txt = "apple chuanchuan "#按字母顺序查找“a”和“m”之间的所有小写字符x = re.findall("[a-m]", txt)print(x)
Run:


Summarize and organize python regular expression analysis

Escape character

*

* represents a special sequence (can also be used to escape special characters) For example, match all numbers:

import re

txt = "我今年20岁了"#查找所有数字字符x = re.findall("\d", txt)print(x)
Run return :


Summarize and organize python regular expression analysis

Any symbol

. can be any character (except newline). For example: Search for a sequence starting with "he", followed by two (any) characters and an "o"

import re

txt = "hello world"#搜索以“he”开头、后跟两个(任意)字符和一个“o”的序列x = re.findall("he..o", txt)print(x)
Running returns:


Summarize and organize python regular expression analysis

Start symbol

^ symbol is used to match the beginning.

import re

txt = "川川菜鸟 飞起来了"x = re.findall("^川", txt)if x:
  print("哇,我匹配到了")else:
  print("哎呀,匹配不了啊")
Run:


Summarize and organize python regular expression analysis

结束符

$ 符号用于匹配结尾,例如:匹配字符串是否以“world”结尾

import re

txt = "hello world"#匹配字符串是否以“world”结尾x = re.findall("world$", txt)if x:
  print("匹配成功了耶")else:
  print("匹配不到哦")

运行:
Summarize and organize python regular expression analysis

星号符

  • 星号符用于匹配零次或者多次出现。
import re

txt = "天上飞的是菜鸟,学python找川川菜鸟!"#检查字符串是否包含“ai”后跟 0 个或多个“x”字符:x = re.findall("菜鸟*", txt)print(x)if x:
  print("匹配到了!")else:
  print("气死了,匹配不到啊")

运行:
Summarize and organize python regular expression analysis

加号符

+ 用于匹配一次或者多次出现
例如:检查字符串是否包含“菜鸟”后跟 1 个或多个“菜鸟”字符:

import re

txt = "飞起来了,菜鸟们!"#检查字符串是否包含“菜鸟”后跟 1 个或多个“菜鸟”字符:x = re.findall("菜鸟+", txt)print(x)if x:
  print("匹配到了!")else:
  print("烦死了,匹配不到")

运行:
Summarize and organize python regular expression analysis

集合符号

{} 恰好指定的出现次数
例如:检查字符串是否包含“川”两个

import re

txt = "川川菜鸟并不菜!"#检查字符串是否包含“川”两个x = re.findall("川{2}", txt)print(x)if x:
  print("匹配到了两次的川")else:
  print("匹配不到啊,帅哥")

返回:
Summarize and organize python regular expression analysis

或符

| 匹配两者任一
例如:匹配字符串菜鸟或者是我了

import re

txt = "菜鸟们学会python了吗?串串也是菜鸟啊!"x = re.findall("菜鸟|是我了", txt)print(x)if x:
  print("匹配到了哦!")else:
  print("匹配失败")

运行:
Summarize and organize python regular expression analysis

特殊序列

指定字符

\A : 如果指定的字符位于字符串的开头,则返回匹配项。
例如:匹配以菜字符开头的字符

import re

txt = "菜鸟在这里"x = re.findall("\A菜", txt)print(x)if x:
  print("是的匹配到了")else:
  print("匹配不到")

运行:
Summarize and organize python regular expression analysis

指定开头结尾

\b 返回指定字符位于单词开头或结尾的匹配项 (开头的“r”确保字符串被视为原始字符串)。
例如:匹配爱开头

import re

txt = "爱你,川川"x = re.findall(r"\b爱", txt)print(x)if x:
  print("匹配到了")else:
  print("匹配不到")

运行:
Summarize and organize python regular expression analysis
又例如:匹配川结尾

import re

txt = "爱你,川川"x = re.findall(r"川\b", txt)print(x)if x:
  print("匹配到了")else:
  print("匹配不到")

运行:
Summarize and organize python regular expression analysis

匹配中间字符

\B 返回存在指定字符但不在单词开头(或结尾)的匹配项 (开头的“r”确保字符串被视为“原始字符串”)
比如我匹配菜鸟:

import re

txt = "我是菜鸟我是菜鸟啊"#检查是否存在“ain”,但不是在单词的开头:x = re.findall(r"\菜鸟", txt)print(x)if x:
  print("匹配到了嘛!!")else:
  print("匹配不到哇!")

运行:
Summarize and organize python regular expression analysis
但是你匹配结尾就会返回空,比如我匹配鸟:

import re

txt = "川川菜鸟"#检查是否存在“鸟”,但不是在单词的末尾:x = re.findall(r"鸟\B", txt)print(x)if x:
  print("匹配到了哦")else:
  print("找不到")

运行:
Summarize and organize python regular expression analysis

匹配数字

\d 返回字符串包含数字(0-9 之间的数字)的匹配项。
例如:

import re

txt = "我今年20岁了啊"#检查字符串是否包含任何位数(0-9的数字)x = re.findall("\d", txt)print(x)if x:
  print("哇哇哇,匹配到数字了")else:
  print("找不到哦")

运行:
Summarize and organize python regular expression analysis

匹配非数字

\D 返回字符串不包含数字的匹配项
例如:

import re

txt = "我今年20岁"#匹配任何非数字符号x = re.findall("\D", txt)print(x)if x:
  print("匹配到了,开心!")else:
  print("匹配不到,生气")

运行:
Summarize and organize python regular expression analysis

空格匹配

\s 返回一个匹配字符串包含空白空间字符的匹配项。
例如:

import re

txt = "我 是 川 川 菜 鸟"#匹配任何空格字符x = re.findall("\s", txt)print(x)if x:
  print("匹配到了")else:
  print("匹配不到啊")

运行:
Summarize and organize python regular expression analysis

匹配非空格

\S 返回字符串不包含空格字符的匹配项

import re

txt = "菜鸟是  我  了"#匹配任意非空字符x = re.findall("\S", txt)print(x)if x:
  print("匹配到了!")else:
  print("匹配不到啊")

运行:
Summarize and organize python regular expression analysis

匹配任意数字和字母

返回一个匹配,其中字符串包含任何单词字符(从 a 到 Z 的字符,从 0 到 9 的数字,以及下划线 _ 字符)
例如:

import re

txt = "菜鸟啊 是串串呀"#在每个单词字符(从a到z的字符,0-9的数字)返回匹配项,以及下划线_字符):x = re.findall("\w", txt)print(x)if x:
  print("匹配到了啊")else:
  print("匹配不到哇")

运行:
Summarize and organize python regular expression analysis

匹配任意非数字和字母

返回字符串不包含任何单词字符的匹配项,在每个非单词字符中返回匹配(不在A和Z之间的字符。“!”,“?”空白位等)
例如:

import re

txt = "菜鸟 是 我嘛?我不信!!"#在每个非单词字符中返回匹配(不在A和Z之间的字符。“!”,“?”空白位等):x = re.findall("\W", txt)print(x)if x:
  print("匹配到了!")else:
  print("匹配不到啊")

运行:
Summarize and organize python regular expression analysis

匹配结尾

\Z 如果指定的字符位于字符串的末尾,则返回匹配项。
例如:

import re

txt = "川川是菜鸟啊"x = re.findall("啊\Z", txt)print(x)if x:
  print("匹配到了哦!")else:
  print("匹配不到")

集合套装

指定符范围匹配

例如集合:[arn]

import re

txt = "The rain in Spain"x = re.findall("[arn]", txt)print(x)if x:
  print("匹配到了!")else:
  print("匹配不到")

匹配任意范围内小写字母

返回任何小写字符的匹配项,按字母顺序在 a 和 n 之间。
例如:

import re

txt = "hello wo r l d"x = re.findall("[a-n]", txt)print(x)if x:
  print("匹配到了!")else:
  print("匹配不到")

运行:
Summarize and organize python regular expression analysis
同样的道理,依次其它情况如下:

[^arn] 返回除 a、r 和 n 之外的任何字符的匹配项

[0123] 返回存在任何指定数字(0、1、2 或 3)的匹配项

[0-9] 返回 0 到 9 之间任意数字的匹配项

[0-5][0-9] 返回 00 到 59 中任意两位数的匹配项

[a-zA-Z] 按字母顺序返回 a 和 z 之间的任何字符的匹配,小写或大写

[+] 在集合中,+, *, ., |, (), $,{} 没有特殊含义,所以 [+] 的意思是:返回字符串中任意 + 字符的匹配项。这个我i举个例子:

import re

txt = "5+6=11"#检查字符串是否有任何 + 字符:x = re.findall("[+]", txt)print(x)if x:
  print("匹配到了")else:
  print("匹配不到")

运行:
Summarize and organize python regular expression analysis

匹配对象

匹配对象是包含有关搜索和结果的信息的对象。注意:如果没有匹配,None将返回值,而不是匹配对象。
直接举个例子:
执行将返回匹配对象的搜索

import re#search() 函数返回一个 Match 对象:txt = "hello world"x = re.search("wo", txt)print(x)

运行:
Summarize and organize python regular expression analysis

Match 对象具有用于检索有关搜索和结果的信息的属性和方法:

span()返回一个包含匹配开始和结束位置的元组。
string返回传递给函数的字符串
group()返回字符串中匹配的部分

span函数

例如:打印第一个匹配项的位置(开始和结束位置)。正则表达式查找任何以大写“S”开头的单词:

import re#搜索单词开头的大写“S”字符,并打印其位置txt = "The rain in Spain"x = re.search(r"\bS\w+", txt)print(x.span())

运行:
Summarize and organize python regular expression analysis

string函数

例如:打印传递给函数的字符串

import re#返回字符串txt = "The rain in Spain"x = re.search(r"\bS\w+", txt)print(x.string)

group函数

例如:打印字符串中匹配的部分。正则表达式查找任何以大写“S”开头的单词

import re#搜索单词开头的大写“w”字符,并打印该单词:txt = "hello world"x = re.search(r"\bw\w+", txt)print(x.group())

运行:
Summarize and organize python regular expression analysis
注意:如果没有匹配,None将返回值,而不是匹配对象。

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