def validate_no_cname(self):
        return
        # There are preexisting records that break this rule. We can't support
        # this requirement until those records are fixed
        if CNAME.objects.filter(fqdn=self.name).exists():
            raise ValidationError("PTR records must point back to a valid A "
                                  "record, not a alias defined by a CNAME."
                                  " -- RFC 1034")
This method returns the symbols in the object, excluding those
dataset/ETHPy150Open rtucker-mozilla/mozilla_inventory/mozdns/ptr/models.py/PTR.validate_no_cname--crossover with--dataset/ETHPy150Open sympy/sympy/sympy/series/sequences.py/SeqBase.free_symbols