def formatted_constituent_array(constituent_array):
    """
    Given a constituent array of Species, return the classic CALPHAD-style interaction.

    Parameters
    ----------
    constituent_array : list
        List of sublattices, which are lists of Species in that sublattice

    Returns
    -------
    str
        String of the constituent array formatted in the classic CALPHAD style

    Examples
    --------
    >>> from pycalphad import variables as v
    >>> const_array = [[v.Species('CU'), v.Species('MG')], [v.Species('MG')]]
    >>> formatted_constituent_array(const_array)
    'CU,MG:MG'

    """
    return ':'.join([','.join([sp.name for sp in subl]) for subl in constituent_array])