python-magic-file

Small Python module to aid developers in getting file extensions from files.

Purpose

The main motivation behind this package is to easily get the file extension from given file instead of trusting the arbitrary file extension in the filename, for example in a web application which accepts file uploads.

Usage

Some examples on how to use this module.

Get extension from file

from python_magic_file import MagicFile

file_path = 'path/to/file'

with open(file_path 'rb') as f:
    magic_file = MagicFile(f)
    extension = magic_file.get_extension()

Get extensions from file

from python_magic_file import MagicFile

file_path = 'path/to/file'

with open(file_path 'rb') as f:
    magic_file = MagicFile(f)
    extensions = magic_file.get_extensions()

Register unknown/non-standard mimetypes

There may be some cases where get_extension() emits a following warning:

UserWarning: File extension for mimetype "video/x-m4v" is None, consider adding an extension for this mimetype using MagicFile.

We have to register file extension using MagicFile.add_type_to_mimetypes_module for video/x-m4v so get_extension() returns the registered extension instead of None.

MagicFile.add_type_to_mimetypes_module simply just calls mimetypes.add_type.

from python_magic_file import MagicFile

# A dictionary of mimetype/extension pairs
new_types = {'video/x-m4v': '.m4v'}

for mimetype, extension in new_types.items():
    MagicFile.add_type_to_mimetypes_module(mimetype, extension)

with open('path/to/m4v-file.m4v', 'rb') as f:
    magic_file = MagicFile(f)
    extension = magic_file.get_extension() # .m4v

Get human readable name for file

from python_magic_file import MagicFile

file_path = 'path/to/file.txt'

with open(file_path 'rb') as f:
    magic_file = MagicFile(f)
    human_readable_name = magic_file.get_name() # ASCII text, with no line terminators

Usage with Flask

import os

from flask import Flask, request, abort
from python_magic_file import MagicFile

from werkzeug.utils import secure_filename
from werkzeug.security import safe_join

app = Flask(__name__)

# Allowed extensions for file uplaod
UPLOAD_ALLOWED_EXTENSIONS = ('.jpg', '.jpeg', '.png')

@app.post('/upload')
def upload_file():
    uploaded_file = request.files.get('file')

    if uploaded_file is None:
        abort(400)

    extension = MagicFile(uploaded_file.stream).get_extension()
    
    if extension not in UPLOAD_ALLOWED_EXTENSIONS:
        abort(400)

    filename, _ = os.path.splitext(secure_filename(uploaded_file.filename))

    save_path = safe_join(os.getcwd(), filename + extension)

    uploaded_file.save(save_path)

    return 'OK'

if __name__ == '__main__':
    app.run()