file signature checker example

import pathlib
import glob


def check(pattern):
    signatures = {
        'jpg': bytes([255, 216, 255]),
        'png': bytes([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]),
        }
    read_size = max(len(sig) for sig in signatures.values())
    for file in glob.glob(pattern):
        file = pathlib.Path(file)
        if not file.is_file():
            continue
        with file.open('rb') as fd:
            data = fd.read(read_size)
        for extension, signature in signatures.items():
            if data.startswith(signature):
                print('{} is a {} file.'.format(file, extension))


check('Downloads/*')