What You'll Learn: In this tutorial, you'll discover how to use the re.sub() function to replace one or many matches of a pattern in a string with another string. This function is useful for editing and cleaning up text.

Syntax

The syntax of the re.sub() function is:

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

Parameters

• pattern (required): The pattern to be found in the string.
• repl (required): The value to replace in the string in place of the matched pattern.
• string (required): The string in which the replacement is to be done.
• count (optional): The maximum number of pattern occurrences to be replaced.
• flags (optional): Optional flags like re.IGNORECASE.

Return Value

The function returns a new string with the replacements.

Examples

1. Replace Pattern Matchings with Replacement String

   • Example Code:

     python

     import re
     
     pattern = '[0-9]+'
     string = 'Account Number - 12345, Amount - 586.32'
     repl = 'NN'
     
     print('Original string')
     print(string)
     
     result = re.sub(pattern, repl, string)
     
     print('After replacement')
     print(result)
     

   • Output:

      

     Original string
     Account Number - 12345, Amount - 586.32
     After replacement
     Account Number - NN, Amount - NN.NN
     

2. Limit Maximum Number of Replacements

   • Example Code:

     python

     import re
     
     pattern = '[0-9]+'
     string = 'Account Number - 12345, Amount - 586.32'
     repl = 'NN'
     
     print('Original string')
     print(string)
     
     result = re.sub(pattern, repl, string, count=2)
     
     print('After replacement')
     print(result)
     

   • Output:

      

     Original string
     Account Number - 12345, Amount - 586.32
     After replacement
     Account Number - NN, Amount - NN.32
     

3. Using Optional Flags

   • Example Code:

     python

     import re
     
     pattern = '[a-z]+'
     string = 'Account Number - 12345, Amount - 586.32'
     repl = 'AA'
     
     print('Original string')
     print(string)
     
     result = re.sub(pattern, repl, string, flags=re.IGNORECASE)
     
     print('After replacement')
     print(result)
     

   • Output:

      

     Original string
     Account Number - 12345, Amount - 586.32
     After replacement
     AA AA - 12345, AA - 586.32
     

Try It Yourself: Fun Exercises

1. Edit Your Favorite Quote:
   • Take a favorite quote and use re.sub() to replace specific words.
2. Clean Up Text:
   • Create a string with messy text and use re.sub() to replace unwanted characters.

Summary:

In this Python tutorial, we learned how to use the re.sub() function to replace matches of a given pattern in a string with a replacement string. This function is powerful for editing and cleaning up text. Keep experimenting and have fun with Python!