


Introduction to the re module and regular expressions in python (with code)
This article brings you an introduction to the re module and regular expressions in Python (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
Regular expression (English: Regular Expression, often abbreviated as regex, regexp or RE in code), also known as regular expression, regular expression, regular expression, regular expression, regular expression, is A concept in computer science. Regular expressions use a single string to describe and match a series of strings that match a certain syntax rule. In many text editors, regular expressions are often used to retrieve and replace text that matches a certain pattern.
Regular expression rules, single character matching
Character | Function | Regular expression example | Match matching example |
---|---|---|---|
Match any character (except n) | b.b | bab,b2b | |
Matches any character from the character set in [] | i [abCde]m | i am | |
Matches any decimal digit, consistent with [0-9] | w\dcschool | w3cschool | |
matches non-numbers, that is, not numbers | mou\Dh | mouth | |
Matches any space character, same as [\n\t\r\v\f] | i\slike | i like | |
Matches any non-whitespace character, as opposed to \s | n\Se | noe,n3e | |
Matches any alphanumeric character, same as [A-Za-z0-9_] | [A-Za-z]w | ||
Matches non-word characters | [0-9]\W[A-Z] | 3 A |
function | regular expression example | matching example | ||
---|---|---|---|---|
a* | aaa | |||
a | aaa | |||
a? | a or b |
##{m} |
||
[0-9]{5 } | 12345 |
{m.} |
||
a{5.} | aaaaa | ##{m,n} | matches the previous one Characters appear from m to n times ||
aaa |
Represents boundary matching |
Characters
^ | ||
---|---|---|
$ | Match the ending part of the string | |
b | Match any word boundary | |
B | Match non-word boundaries | |
##Match groups |
##\ | matches either left or right The expression ||
---|---|---|
##(ab) | treats the characters in brackets as a group | |
\num | Reference the string matched by group num | |
(?P< ;name>) | Group alias | |
(?P=name) | The reference alias is name Group matched strings | |
re module | In python, you can use the built-in re module Regular expression | Common functions and methods of re module
compile(pattern,flags=0) | Compiles the regular expression pattern using any optional flags, then returns a regular expression object |
---|
re module functions and regular expression object methods | Description |
---|---|
match(pattern, string,flags=0) | Attempts to match a string using a regular expression pattern with optional flags. If the match is successful, return the matching object; if it fails, return None |
search(pattern,string,flags=0) | Search for string using optional flags The first occurrence of the regular expression pattern in . If the match is successful, the matching object is returned; if it fails, None is returned. |
findall(pattern,string,[,flags]) | Find all occurrences in the string regular expression and returns a list |
split(pattern,string,max=0) | According to the pattern separator of the regular expression, the split function separates the characters Split the string into a list, and then return a list of successful matches. The split operation can be max times (the default is to split all successfully matched positions) |
Use repl to replace all occurrences of the regular expression pattern in the string. Unless count is defined, all occurrences will be replaced. |
Description | |
---|---|
Default returns the entire matching object or returns a specific subgroup numbered num | |
Returns a tuple containing all matching subgroups, If there is no successful match, an empty tuple is returned | |
Explanation | |
---|---|
Make the match case-insensitive (ignore case) | |
.(dot) matches anything except n All characters except, re.S mark indicates. (dot) can match all characters | ##re.M |
re.U | |
re.X | |
- compile()
- function to convert the regular expression The string form is compiled into a regular expression object;
matches the text through a series of methods provided by the regular expression object (such as: match() - ) Search and obtain the matching result, a
Match
Finally use the properties and methods provided by theobject;
Match - object (for example:
group ()
re module usage example) Obtain information and perform other operations as needed.
Import module
import recompile()
Function compile function is used to compile regular expressions and generate a Pattern object. Its general usage form is as follows:
import re
# 将正则表达式编译成pattern对象
pattern = re.compile(r'\d+')
After compiling into a regular expression object, you can use the regular expression mentioned above expression object method.
Method The match method is used to find the head of the string (you can also specify the starting position), it is
once Matching, as long as a matching result is found, it is returned instead of searching for all matching results. Its general usage form is as follows:
match(string[, pos[, endpos]])
Among them, string is the string to be matched, pos and endpos are optional parameters, specifying the
start and endpoint# of the string. ## position, the default values are 0 and len
(string length) respectively. Therefore, when you do not specify pos and endpos, the match method defaults to matching the head of the string. When the match is successful, a Match object is returned. If there is no match, None is returned.
<pre class="brush:php;toolbar:false">>>> import re
>>>
>>> pattern = re.compile(r'\d+') # 正则表达式表示匹配至少一个数字
>>>
>>> m = pattern.match("one2three4") # match默认从开头开始匹配,开头是字母o,所以没有匹配成功
>>> print(m) # 匹配失败返回None
None
>>>
>>> m = pattern.match("1two3four") # 开头字符是数字,匹配成功
>>> print(m)
<_sre.sre_match>
>>>
>>> m.group() # group()方法获取匹配成功的字符
'1'
>>> m = pattern.match("onetwo3four56",6,12) # 指定match从数字3开始查找,第一个是数字3,匹配成功
>>> print(m)
<_sre.sre_match>
>>> m.group()
'3'</_sre.sre_match></_sre.sre_match></pre>
The above is the detailed content of Introduction to the re module and regular expressions in python (with code). For more information, please follow other related articles on the PHP Chinese website!

This article aims to provide a Python script for reading data from a CSV file and calculating the office hours corresponding to each ID within a specific month (such as February). The script does not rely on the Pandas library, but uses the csv and datetime modules for data processing and time calculation. The article will explain the code logic in detail and provide considerations to help readers understand and apply the method.

When initializing using PyTerrier, users may encounter a ssl.SSLCertVerificationError error, prompting certificate verification failed. This is usually caused by the system's inability to obtain or verify the local issuer certificate. This article will explain the causes of this problem in detail and provide a way to quickly resolve the problem by temporarily disabling SSL certificate verification, while highlighting its potential security risks and applicable scenarios.

This article describes how to use Python to crop a value in a list so that it falls within a specified upper and lower limit range. We will explore two implementation methods: one is an intuitive method based on loops, and the other is a concise method that uses min and max functions. Help readers understand and master numerical cropping techniques with code examples and detailed explanations, and avoid common mistakes.

This article aims to resolve the "y contains previously unseen labels" error encountered when encoding data using LabelEncoder. This error usually occurs when there are different category tags in the training set and the test set (or validation set). This article will explain the causes of the error in detail and provide the correct encoding method to ensure that the model can handle all categories correctly.

This tutorial aims to solve the problem of sorting numeric columns in Pandas DataFrame and inserting rows containing strings on top of the sorted DataFrame. We will explain how to create a DataFrame with mixed data types, sort it, and then insert new lines containing strings, and provide complete code examples and detailed step instructions to help readers master the skills to deal with similar problems in Pandas.

This tutorial explains in detail how to efficiently calculate the accumulated sum of a column in a Pandas DataFrame and add its results to the DataFrame as a new column. We will use Pandas' built-in cumsum() method to demonstrate how to implement row-level continuous summing operations through concise Python code examples, thereby simplifying the data processing process and improving data analysis efficiency.

This article explains in detail how to efficiently add new parameters to existing JSON data (such as user inventory) in Discord robot applications. By optimizing file reading and writing strategies, inefficient in-loop file operations are avoided, and data is modified and persisted in one-time in memory is realized, which significantly improves update efficiency and system performance, ensuring the accuracy and reliability of data updates.

This article discusses the method to implement F-bounded polymorphism in Python type prompts, that is, how to make the base class method return the type of its specific subclass. In view of the limitations encountered by traditional TypeVar when referencing its own subclasses, the article details the typing.Self type, showing how it gracefully solves this problem, ensures the accurate delivery of type information, and provides two implementation examples based on instance methods and class methods.


Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Dreamweaver Mac version
Visual web development tools

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

SublimeText3 English version
Recommended: Win version, supports code prompts!