Return a default filename prefix for output files based on the input files.

    :param filenames:
        The input filename(s):

    :type filenames:
        str or list of str

    :returns:
        The extensionless common prefix of the input filenames:

    :rtype:
        str

def _default_output_prefix(filenames):
    """
    Return a default filename prefix for output files based on the input files.

    :param filenames:
        The input filename(s):

    :type filenames:
        str or list of str

    :returns:
        The extensionless common prefix of the input filenames:

    :rtype:
        str
    """

    if isinstance(filenames, (str, )):
        filenames = [filenames]
    common_prefix, ext = os.path.splitext(os.path.commonprefix(
        map(os.path.basename, filenames)))
    common_prefix = common_prefix.rstrip("_-")
    return common_prefix if len(common_prefix) > 0 else "sick"