def _format_defaults(value):
    """
    Format value to CLI syntax.

    Example usage: if default value of a parameter is ['gene'], the description
    in CLI would be::

        (default: ['gene'])

    After using this function the description is tailored to CLI usage::

        (default: gene)
    """
    if isinstance(value, list):
        return ' '.join(value)
    else:
        return value