def extract_header(filename: str):
    """ Extract the header of a Deltamed .eeg file.

    Args:
        filename: path to the .eeg file.
    Returns:
        A list of bytes
    """
    header = []

    with open(filename, 'rb') as file_:
        header = [
            char if isinstance(char, bytes) else bytes([char])
            for char in file_.read(720)
        ]
    return header