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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _proc_no_rot_sym(self):
 """ Handles molecules with no rotational symmetry. Only possible point groups are C1, Cs and Ci. """

        self.sch_symbol = "C1"
        if self.is_valid_op(PointGroupAnalyzer.inversion_op):
            self.sch_symbol = "Ci"
            self.symmops.append(PointGroupAnalyzer.inversion_op)
        else:
            for v in self.principal_axes:
                mirror_type = self._find_mirror(v)
                if not mirror_type == "":
                    self.sch_symbol = "Cs"
                    break