Regex Backreferences in Python

Regex backreferences are a powerful tool for working with complex patterns and extracting data from strings. In this tutorial, we will explore how to use backreferences in Python to match and capture patterns in strings, as well as some practical use cases for this technique. Whether you are a beginner or an experienced Python user, regex backreferences can significantly enhance your ability to manipulate and analyze data with regular expressions.

Python Regex Backreferences :

• Backreferences are a feature of Python's regular expression syntax that allow you to refer to previously matched expressions.
• They are used to identify repeated patterns in text and can be used to extract specific parts of a text.
• To create a backreference, use a backslash followed by a number that corresponds to the capturing group you want to reference.
• Code Sample :

import re

# Backreference example
text = "The quick brown fox jumps over the lazy dog."
pattern = r"\b(\w+)\s+\1"
result = re.findall(pattern, text)
print(result)  


# Output: 
['the', 'lazy']

Get Text Inside Quotes using Python Regex Backreferences :

• Backreferences can be used to extract text inside quotes.
• To do this, you can use a 
  • regular expression pattern that matches a quote, 
  • followed by any number of non-quote characters, 
  • followed by the same quote character.
• Code Sample :

import re

# Backreference example to extract text inside quotes
text = 'The "quick brown" fox jumps over the "lazy dog".'
pattern = r'"([^"]*)"'
result = re.findall(pattern, text)
print(result) 


 # Output: 
 ['quick brown', 'lazy dog']
 
 
 
 

Words with consecutive Repeated Character :

• Backreferences can also be used to identify words that have at least one consecutive repeated character.
• To do this, you can use a 
  • regular expression pattern that matches any word character, 
  • followed by the same character, 
  • and then any additional word characters.
• Code Sample :

import re

# Backreference example to find words with repeated characters
text = "She sells seashells by the seashore."
pattern = r"\b(\w)(\w)\1"
result = re.findall(pattern, text)
print(result)  

# Output: 
[('s', 'e'), ('l', 'l'), ('s', 'h'), ('l', 'l'), ('s', 'e'), ('s', 's'), ('s', 'e'), ('s', 'h'), ('r', 'e')]