docs: def write_group(self, grp, overwrite=False, **kwargs):
          """
          Write the concatenated alignment to disk in the location specified by
          self.cache_dir
          """
          id_ = self.get_id(grp)
          alignment_done, result_done = self.check_work_done(grp)
          self.cache[grp] = id_
          al_filename = os.path.join(self.cache_dir, '{}.phy'.format(id_))
          qfile_filename = os.path.join(self.cache_dir, '{}.partitions.txt'.format(id_))
          if overwrite or not (alignment_done or result_done):
              conc = self.collection.concatenate(grp)
              al = conc.alignment
              al.write_alignment(al_filename, 'phylip', True)
              q = conc.qfile(**kwargs)
              with open(qfile_filename, 'w') as fl:
                  fl.write(q + '\n')