How can I check the extension of a file?

python

file-handling

pathlib

file-extension

byAlex Kataev·Feb 9, 2025

The os.path.splitext() function in Python splits the filename into its name and extension:

import os

# Get extension of 'example.txt' or 'final_draft_v2_FINAL.txt'
print(os.path.splitext('example.txt')[1])  # Output: .txt

This snippet is a direct and efficient way to extract just the extension.

We can add case-insensitivity and multi-extension handling for an enhanced file extension check:

filename = 'example.TXT'
extension = os.path.splitext(filename)[1].lower()  # Normalize to lowercase
if extension == '.txt':
    print("Found a TXT. The Treasure-X-Trove.")
elif extension in ('.jpg', '.jpeg', '.png'):
    print("Look, a wild Image file appears!")

Extracting an extension with pathlib

Use pathlib for a modern and cleaner approach to file handling in Python:

from pathlib import Path

# Using pathlib to get the file extension
file_path = Path('example.txt')
if file_path.suffix.lower() == '.txt':
    print(f"The file {file_path.name} may contain secrets.")

Pathlib can also differentiate files from directories, ensuring you aren't trying to read a folder as if it were a user manual.

Finding a pattern with fnmatch

To check multiple similar extensions, use the fnmatch module for its pattern matching capabilities:

import fnmatch
import os

for file in os.listdir('.'):
    if fnmatch.fnmatch(file, '*.txt'):
        print(f"{file} - Doctor, we've got a txt!")

Pattern recognition with glob

The glob module simplifies fetching files by their extensions, even from nested directories:

import glob

# Retrieve all .txt files in the current directory
text_files = glob.glob('*.txt')
for file in text_files:
    print(f"{file}: Why can't a bicycle stand up by itself? Because it's two-tired.")

Because, why not throw in a bicycle pun while traversing a directory?

A smarter way to handle file types

To streamline code logic and avoid an ugly if-elif chain when dealing with various types of files, use this clever trick:

file_ext_actions = {
    '.txt': process_text_file,  # Whisperer of Text Files
    '.jpg': process_image_file,  # JPEG Janitor
    '.png': process_image_file,  # PNG Paramedic
    '.pdf': process_pdf_file,  # PDF Pirate
}

file_ext = os.path.splitext('example.txt')[1]  # Extracting the life purpose of a file
action = file_ext_actions.get(file_ext.lower())  # Deciding its fate...
if action:
    action()  # Unleashing the file to its destined path
else:
    print("Unsupported file type. Maybe we're just too advanced?")