def format_persec_column_label(label):
    """ Return a re-formatted PerSecData column label

    This function converts column labels to snake case (all lower-case
    and spaces converted to underscores).

    Parameters
    ----------
    label: str
        The original column label to be formatted

   Returns
   -------
   formatted_label: str
        The formatted label
    """
    assert isinstance(label, str)

    formatted_label = label.lower().replace(' ', '_')

    assert formatted_label.islower() and ' ' not in formatted_label

    return formatted_label