import hashlib


def checksum_file(scheme, path):
    """Return the checksum (hex digest) of a file"""
    h = getattr(hashlib, scheme)()
    
    with open(path, 'rb') as f:
        chunk = f.read(65535)
        while chunk:
            h.update(chunk)
            chunk = f.read(65535)
    return h.hexdigest()