Python Match.re Attribute

last modified April 20, 2025

Introduction to Match.re

The Match.re attribute is a property of match objects in Python's re module. It returns the regular expression pattern object used for the match.

This attribute provides access to the original compiled pattern that produced the match. It's useful when you need to inspect or reuse the pattern that created a particular match object.

The Match.re attribute connects match results back to their source pattern, enabling more dynamic regex processing and debugging.

Basic Definitions

A Match object is returned by successful regex operations like search and match. It contains match details.

The re attribute of a Match object references the compiled regex pattern (Pattern instance) that produced the match.

Accessing the Original Pattern

This basic example shows how to access the original pattern from a match.

basic_re_access.py

#!/usr/bin/python

import re

text = "The year is 2023"
pattern = re.compile(r'\d{4}')

match = pattern.search(text)
if match:
    print("Matched text:", match.group())
    print("Original pattern:", match.re.pattern)

This demonstrates accessing the original pattern string through the Match.re attribute. The pattern property of the regex object contains the original pattern string.

match = pattern.search(text)

We perform a search operation that returns a match object if successful. The match object contains information about where the pattern was found.

print("Original pattern:", match.re.pattern)

Here we access the original pattern string through the match object's re attribute. This shows the exact pattern that produced the match.

Inspecting Pattern Flags

The Match.re attribute also lets you inspect the flags used.

flag_inspection.py

#!/usr/bin/python

import re

text = "Case INSENSITIVE match"
pattern = re.compile(r'insensitive', re.IGNORECASE)

match = pattern.search(text)
if match:
    print("Matched text:", match.group())
    print("Pattern flags:", match.re.flags)
    print("IGNORECASE flag set?", bool(match.re.flags & re.IGNORECASE))

This example shows how to check which flags were used in the original pattern. The flags property contains all active flags.

Reusing the Original Pattern

You can reuse the original pattern from a match for further operations.

pattern_reuse.py

#!/usr/bin/python

import re

text = "First match: apple, second match: orange"
pattern = re.compile(r'\b\w{5}\b')  # Match 5-letter words

first_match = pattern.search(text)
if first_match:
    print("First match:", first_match.group())
    
    # Use the same pattern to find next match
    second_match = first_match.re.search(text, first_match.end())
    if second_match:
        print("Second match:", second_match.group())

This demonstrates how to reuse the original pattern from a match object to perform additional searches. The pattern remains accessible through the match's re attribute.

Debugging with Match.re

The Match.re attribute is useful for debugging regex patterns.

debugging.py

#!/usr/bin/python

import re

def debug_match(match):
    if match:
        print("Match successful!")
        print("Matched text:", match.group())
        print("Pattern used:", match.re.pattern)
        print("Pattern flags:", match.re.flags)
    else:
        print("No match found")

text = "Debug this pattern: 123-456-7890"
pattern = re.compile(r'\d{3}-\d{3}-\d{4}')

match = pattern.search(text)
debug_match(match)

This example shows how Match.re can help debug regex operations by providing access to the original pattern and flags.

Dynamic Pattern Inspection

You can dynamically inspect and modify behavior based on the original pattern.

dynamic_inspection.py

#!/usr/bin/python

import re

def process_match(match):
    original_pattern = match.re.pattern
    
    if 'email' in original_pattern:
        return "[EMAIL REDACTED]"
    elif 'phone' in original_pattern:
        return "[PHONE REDACTED]"
    else:
        return match.group()

text = "Contact: email@example.com or 555-123-4567"
email_pattern = re.compile(r'email\s*:\s*(\S+@\S+)')
phone_pattern = re.compile(r'phone\s*:\s*(\d{3}-\d{3}-\d{4})')

email_match = email_pattern.search(text)
if email_match:
    print(process_match(email_match))

phone_match = phone_pattern.search(text)
if phone_match:
    print(process_match(phone_match))

This advanced example demonstrates using Match.re to make processing decisions based on the original pattern that produced a match.

Comparing Patterns

You can compare patterns from different matches using the Match.re attribute.

pattern_comparison.py

#!/usr/bin/python

import re

text = "apple orange banana"
fruit_pattern = re.compile(r'\b\w{5}\b')
color_pattern = re.compile(r'\b\w{6}\b')

fruit_match = fruit_pattern.search(text)
color_match = color_pattern.search(text)

if fruit_match and color_match:
    print("Same pattern used?", fruit_match.re is color_match.re)
    print("Fruit pattern:", fruit_match.re.pattern)
    print("Color pattern:", color_match.re.pattern)

This example shows how to compare whether two matches came from the same original pattern by comparing their re attributes.

Accessing Pattern Methods

Through Match.re, you can access all pattern object methods.

pattern_methods.py

#!/usr/bin/python

import re

text = "Sample text with 3 numbers: 1, 2, and 3"
pattern = re.compile(r'\d')

match = pattern.search(text)
if match:
    print("First number:", match.group())
    
    # Use findall from the original pattern
    all_numbers = match.re.findall(text)
    print("All numbers:", all_numbers)

This demonstrates accessing pattern methods like findall through the Match.re attribute after an initial match.

Best Practices

When working with Match.re, consider these best practices:

Use it for debugging to verify which pattern produced a match
Access pattern flags when match behavior needs verification
Reuse the pattern for subsequent matches when appropriate
Document pattern dependencies when storing match objects
Prefer direct pattern references when possible for clarity

Performance Considerations

Accessing Match.re has minimal overhead since it's just a reference to an existing object. However, unnecessary pattern inspection should be avoided in performance-critical code.

The attribute is most valuable in debugging scenarios or when building dynamic regex processing systems that need to inspect match origins.

Source

Python Match.re documentation

This tutorial covered the essential aspects of Python's Match.re attribute. Understanding this feature enables more advanced regex debugging and dynamic pattern processing in your Python applications.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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