Python replaceall Regex – Tutorial with Examples

Python provides a powerful library called re to work with regex. This article will discuss how to use Python’s re module to perform replaceall functionality using regex, along with various examples and use cases.


The re Module in Python

Python has a built-in library called re that provides support for regular expressions. The re module offers several functions to work with regex, such as search(), match(), findall(), finditer(), sub(), and subn().

Replaceall Functionality with Regex


Using re.sub()

The re.sub() function is used to replace all occurrences of a pattern in a given string. The syntax for re.sub() is:

re.sub(pattern, repl, string, count=0, flags=0)


Here, pattern is the regex pattern, repl is the replacement string, string is the input text, count specifies the maximum number of replacements, and flags allows you to modify the regex behavior.


Using re.subn()

The re.subn() function is similar to re.sub(), but it returns a tuple containing the modified string and the number of substitutions made. The syntax for re.subn() is:

re.subn(pattern, repl, string, count=0, flags=0)

Simple String Replacement

Let’s start with a basic example of replacing all occurrences of a specific word in a given string:

import re

text = "I love Python. Python is a great language."
new_text = re.sub("Python", "Java", text)


I love Java. Java is a great language.


Case Insensitive Replacement

In some cases, you might want to perform a case-insensitive replacement. To do this, you can use the re.IGNORECASE flag:

import re

text = "I love Python. PYTHON is a great language."
new_text = re.sub("python", "Java", text, flags=re.IGNORECASE)


Replacing Multiple Patterns

To replace multiple patterns in a string, you can use the | operator in the regex pattern:

import re

text = "I love cats and dogs."
new_text = re.sub("cats|dogs", "animals", text)


I love animals and animals.


Limiting the Number of Replacements

You can limit the number of replacements by specifying the count parameter:

import re

text = "Apple, Orange, Banana, Orange, Grape, Orange"
new_text = re.sub("Orange", "Mango", text, count=2)


Apple, Mango, Banana, Mango, Grape, Orange


Custom Replacement Function

You can use a custom function for more complex replacements:

import re

def custom_repl(match_obj):
    if == "cat":
        return "dog"
    elif == "dog":
        return "cat"
        return "animal"

text = "I have a cat, a dog, and a parrot."
new_text = re.sub("cat|dog|parrot", custom_repl, text)


I have a dog, a cat, and an animal.



In this article, we covered the replaceall functionality in Python using regex with various examples.

We also discussed some common use cases in enterprise applications. With the power of the re module and regex, you can efficiently manipulate and process text data in your Python projects.

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