def listify(x):
    """Puts non-list objects into a list. 

    Parameters
    ----------
    x: Object to ensure is list
    
    Returns
    ----------
    :obj:`list`
        If ``x`` is already a list, this is returned. Otherwise, a list\
        containing ``x`` is returned.
    """
    if isinstance(x, list):
        return x
    else:
        return [x]