Replacing specific pattern using regex in Python

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by kanika dot icon Updated: May 8, 2023

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Re.sub is a function in Python's re-module. It allows substituting a string pattern with another string. It can replace all pattern occurrences with a specified replacement string. 

We can make different types of substitutions with re.sub are: 

Regular Expression Substitution: 

Replace a character pattern with patterns like ASCII letters or characters. 

String Replacement: 

Replace all occurrences of a string with another string. 

Numeric Substitution: 

Replace all occurrences of a number with another number. 

Character Class Substitution: 

Replace all occurrences of a character class with another character class. 

Re.sub also offers several options for matching and replacing strings. These options include: 

Case-insensitive matching: 

This makes the search case insensitive. It means that we have to match the upper and lowercase letters. 

Range matching: 

This limits the search to a certain range of characters. 

Greedy matching: 

This allows the search to match as many characters as possible. 

Regex matching:

This allows for regex patterns in the search. 

Unicode matching: 

This allows for the search to match Unicode characters. 

The re. sub-Python module helps in performing complex string manipulations and substitutions. It allows developers to search for patterns within strings. Then it can replace them with other characters or strings. It can apply formatting to strings, extract substrings, and more. Re.sub supports regular expressions, a powerful pattern-matching language. It will allow developers to work with complex patterns. It is a tool for text processing, simplifying difficult and time-consuming programming tasks. 

Also, another Python module, "itertools", is a tool collection. It helps assist in working with iterators. It provides functions that allow you to work with iterators quickly. The functions can be chain, product, and zip_longest. These functions enable you to create and manipulate iterators and process data. It will create complex programming tasks. The itertools module also makes it easier to work with generators. It will allow you to create, modify, and manipulate iterators. Using the functions in this module, you can simplify complex programming tasks. It can, in turn, help process data. 

You can make powerful string operations by understanding the use of re.sub. Re.sub is an important tool for improving your Python programming skills. It allows you to make advanced string manipulation and pattern-matching operations. Those are otherwise difficult or impossible in Python. Re.sub can extract patterns from a string, split strings into groups. You can then perform substitutions and more.

With a better understanding of re.sub, you can create complex scripts with fewer lines of code. You can do it by making your code more efficient. Additionally, we use the re.sub in web development and data analysis. So, a better understanding of using it can make you more valuable in the workplace. 

Replacing patterns is often used in text-processing tasks. It can perform search and replace operations. The operations can be data mining, data cleansing, and text mining. It helps identify patterns in large datasets and allows for easier analysis. For example, a medical researcher can use pattern replacement. It will help identify common symptoms of a particular disease. Also, a financial analyst might use pattern replacement. It can help identify recurring financial trends in the stock market. 

Regex (or Regular Expressions) is a way of defining patterns in strings in Python. It is a tool used to search, edit, and manipulate text. Regex can verify that a string contains a given pattern and validate user input. It can help extract information from a string. 

Here is an example of replacing a specific pattern using regex in Python. 


In this solution, we are replacing specific pattern using regex in Python


Follow the steps carefully to get the output easily.

  1. Install Jupyter Notebook on your computer.
  2. Open terminal and install the required libraries with following commands.
  3. Copy the code using the "Copy" button above and paste it into your IDE's Python file.
  4. Remove the last line.
  5. Add a line: print(new_s)
  6. Run the file.

I hope you found this useful. I have added the link to dependent libraries, version information in the following sections.

I found this code snippet by searching for "Replacing specific pattern using regex in Python" in kandi. You can try any such use case!

Dependent Libraries

regexby xysun

Python doticonstar image 92 doticonVersion:Currentdoticon
License: Permissive (MIT)

Regular expression engine in Python using Thompson's algorithm.


            regexby xysun

            Python doticon star image 92 doticonVersion:Currentdoticon License: Permissive (MIT)

            Regular expression engine in Python using Thompson's algorithm.


                      What is a compiled regular expression object, and how does it work with re.sub python?  

                      A compiled RE object is a pre-compiled version of a regular expression pattern. We can parse and analyze it. It is faster than a regular expression pattern string. It is already pre-compiled. With re.sub python, a compiled RE object can perform a search and replace operation on a string. We can pass the compiled regular expression object with a replacement string to re.sub. It will replace all instances of the pattern in the string with the replacement string. 

                      How do I use the match object argument in re.sub python?  

                      The match object argument replaces a regular expression match object. You can use it to search and replace a specific pattern in a string. We can do it with the specified string. 

                      How can I access the regex match objects produced using re.sub python?  

                      You can use the optional argument count in the re.sub() method to limit the number of replacements. Then, we use the re.findall() method to get all the matches. 

                      What can support pattern matches by Python's module for regular expressions (re)?  

                      Python's module for regular expressions supports the patterns. It supports patterns like 

                      • literal strings, 
                      • wildcards, 
                      • character classes, 
                      • sets, 
                      • repetition, 
                      • groupings, 
                      • anchors, 
                      • look-ahead, 
                      • look-behinds, and 
                      • backreferences. 

                      How can I use re.sub to search for zero or more occurrences of a given string?  

                      You can use the following regex expression in re.sub to search for zero or more occurrences of a given string. This expression will match any instance of the given string, including zero occurrences. You can use (string){0,} where "string" is the string you want to search for. 

                      When using re, how do I determine if my data set has a matching substring?  

                      You can use the to find out if there is a matching substring in your data set. The function will search through the string for any substring. It matches the pattern you have specified and returns a match object if we find one. 

                      Does the Unicode support in Python affect how we compare strings when using re functions such as sub()?  

                      No, the Python Unicode support does not affect how we compare the strings. But when we use the re functions like sub(). The re functions will treat strings as raw bytes so that we can treat the Unicode characters like any other byte. 

                      Can I assign a group name to each matching pattern using re-functions like sub()?  

                      You cannot assign a group name to each matching pattern when using re-functions such as sub(). But you can retrieve the matched pattern from the group() method. 

                      What escape sequence should prevent errors when passing strings into functions like sub()?  

                      We can use the escape sequence as "\". This helps escape any special characters in a string. It might otherwise cause errors when passed into a function. 

                      Are there any alternative methods for accessing matches? Which made with regex patterns other than through the sub() function?  

                      Yes, we can use alternative methods for accessing matches with regex patterns. It includes using the findall() function, the search() function, and the split() function. The findall() function searches for all occurrences of a pattern and returns them as a list of strings. The search() function searches for the first pattern occurrence. It will then return a corresponding match object. The split() splits a string into a list of strings based on a given pattern. 

                      If you do not have regex that is required to run this code, you can install it by clicking on the above link and copying the pip Install command from the respective page in kandi.

                      You can search for any dependent library on kandi like regex

                      Environment Tested

                      I tested this solution in the following versions. Be mindful of changes when working with other versions.

                      1. The solution is created in Python 3.9.6
                      2. The solution is tested on re version 2.2.1

                      Using this solution, we are able to replace specific patterns using regex in Python


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