def get_homologs(homologs_fname):
    """Extract the list of homolog structures from a list file

    :param homologs_fname: file name with the list of homologs
    :type homologs_fname: str
    :returns homologs_list containing the pdb codes of the homolog structures in the input file
    :rtype tuple
    """

    homologs_list = []
    with open(homologs_fname, 'r') as fhandle:
        for line in fhandle:
            homologs_list.append(line.rstrip()[:-2].lower())
    return tuple(homologs_list)