def output_T(results, contrast, retvals=('effect', 'sd', 't')):
    """ Convenience function to collect t contrast results

    Parameters
    ----------
    results : object
        implementing Tcontrast method
    contrast : array
        contrast matrix
    retvals : sequence, optional
        None or more of strings 'effect', 'sd', 't', where the presence of the
        string means that that output will be returned.

    Returns
    -------
    res_list : list
        List of results.  It will have the same length as `retvals` and the
        elements will be in the same order as retvals
    """
    r = results.Tcontrast(contrast, store=retvals)
    returns = []
    for valname in retvals:
        if valname == 'effect':
            returns.append(r.effect)
        if valname == 'sd':
            returns.append(r.sd)
        if valname == 't':
            returns.append(r.t)
    return returns