def cdf_chainid_to_stride_chainid(cdf_chainid):
    """
    Convert a CDF (CATH Domall File) chainid to a STRIDE chainid.
    STRIDE uses '-' for a 'blank' chainid while PDB uses ' ' (space)
    and CATH (CDF) uses '0' where PDB has a blank (space) chain identfifer.
    We use the STRIDE convention ('-') in this program.
    So all this does is return the cdf_chainid unless it is '0', then
    it returns '-'.

    Parameters:
        pdb_chainid - the PDB chain identifier
    Return value:
        STRIDE chain identifier corresponding to supplied pdb_chainid
    """
    if cdf_chainid == '0':
        return '-'
    else:
        return cdf_chainid