Why does the escape character / need to be added after r in the regular expression of python?

topic description

The

requirement is to replace the better in text with that strong
in the regular mode of the sub method, where I have added r to indicate escape.
Why add a\, written as r"\ * (. *?)\ *?
Why can"t you just write ringing * (. *?) *?
what do the two here do?

related codes

text = "Beautiful is better than ugly."
re.sub (r"\ * (. *?)\ *," , text)

what result do you expect? What is the error message actually seen?

in the regular mode of the sub method, I have added r in front to indicate escape.
Why add a\, written as r"\ * (. *?)\ *?
Why can"t you just write ringing * (. *?) *?

what I need is between * and *, and I don"t need * to represent the quantity, so why add\ * after r to escape *?

Python regular-expression
May.24,2022

in fact, there are two levels of escape, one is string assignment, the other is regular engine escape

Let's start with r in front of the string. python escapes the escaped characters in the string by default, for example, \ n wraps lines directly. If you want to print \ n , you need to define \ n , while the string is preceded by r , so it will not be escaped. 

>>> print('\n')


>>> print('\\n')
\n
>>> print(r'\n')
\n

besides * , * is not an escaped character in a string, but it has a special meaning for regular expressions. The reason for adding \ * is to make the regular engine think of it as a normal string. If your regular is just a simple r'\ * (. *?)\ * , whether you add r or not, the result is the same. python string assignment will not escape it

. 
>>> print(r'\*(.*?)\*')
\*(.*?)\*
>>> print('\*(.*?)\*')
\*(.*?)\*

Previous: How can flask do multi-table queries without foreign keys?

Next: Phpstrom usage problems

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1bd64e1-3100b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1bd64e1-3100b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?