File Extension Extraction Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching file extension extraction, ported and verified for Python. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# File Extension Extraction
# ReDoS-safe | RegexVault — Dev & Systems > File Paths

import re

file_extension_extraction_pattern = re.compile(r'(?:^|\/)([^\/\s\.]+[\w.]*\.([a-zA-Z0-9]{1,10}))$')

def validate_file_extension_extraction(value: str) -> bool:
    return bool(file_extension_extraction_pattern.fullmatch(value))

# Example
print(validate_file_extension_extraction("file.txt"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > File Paths category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Group 1 = final extension segment. For compound extensions like .tar.gz, extract the last segment (gz). Extension limited to 10 chars. Dotfiles (.gitignore) have no extension.