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Summary: Learn how to dynamically replace text in strings using Python's `re` module. This blog explores several examples of using regular expressions (regex) in Python to perform replace operations.
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How to Replace Text in Python Using Regular Expressions

Working with text often involves finding and replacing patterns rather than fixed substrings. Python’s regex module, re, provides powerful tools for such operations. This guide will guide you through using Python to replace text in strings using regular expressions with several practical examples.

Introduction to re Module

The re module is Python's built-in library for working with regular expressions. Regular expressions (regex) allow for flexible pattern matching, which is essential for complex string manipulations.

To use it, you first need to import the module:

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Basic Replace Using sub()

The re.sub() method is primarily used for replacing patterns in strings. It takes three arguments:

The regex pattern to search for.

The replacement string.

The target string.

Here’s a basic example:

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In this case, the word 'fox' will be replaced by 'cat'.

Replace with a Pattern

What if we want to replace any digit in a string with an asterisk (*)? The same sub() function can be used with a regex pattern:

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This will replace each individual digit with an asterisk:

User*** logged in at *:* PM.

Replace All Occurrences

The re.sub() method replaces all occurrences of the pattern by default. If you have a scenario where you need to replace multiple similar patterns globally across your string, this function is especially useful.

For instance:

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This will replace all occurrences of "apple" and "banana" with "fruit":

fruit, fruit, fruit, orange, fruit, pineapple

Using Group References in Replacement

Regular expressions in Python allow you to use matched groups in the replacement string. Groups are parts of the pattern enclosed in parentheses. Here is an example:

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This will format the number in a more readable way:

John Doe, (123) 456-789

Using Functions for More Complex Replacements

If your replacement decision requires computation, you can pass a function to re.sub(). This function will be called for every match, and its return value will be used as the replacement string.

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This example adds a 10% tax to all dollar amounts in the string:

Price: $11.55, Discount: $1.38

Conclusion

The re module in Python provides powerful tools for replacing text using regular expressions. These basic and advanced techniques will come in handy when you are tasked with dynamic and complex string manipulations.

Experiment with these methods in your projects to get a better understanding and unleash the full power of text processing.