def join(chord_root, quality='', extensions=None, bass=''):
    r"""Join the parts of a chord into a complete chord label.

    Parameters
    ----------
    chord_root : str
        Root pitch class of the chord, e.g. 'C', 'Eb'
    quality : str
        Quality of the chord, e.g. 'maj', 'hdim7'
        (Default value = '')
    extensions : list
        Any added or absent scaled degrees for this chord, e.g. ['4', '\*3']
        (Default value = None)
    bass : str
        Scale degree of the bass note, e.g. '5'.
        (Default value = '')

    Returns
    -------
    chord_label : str
        A complete chord label.

    """
    chord_label = chord_root
    if quality or extensions:
        chord_label += ":%s" % quality
    if extensions:
        chord_label += "(%s)" % ",".join(extensions)
    if bass and bass != '1':
        chord_label += "/%s" % bass
    validate_chord_label(chord_label)
    return chord_label