def _get_core_op_cls(op_type=None):
        """
        A utility function that retrieves an op cls using the curr_opset_version
        """
        if op_type not in SSAOpRegistry.core_ops:
            raise ValueError("op {} not registered.".format(op_type))
        candidate_ops = SSAOpRegistry.core_ops[op_type]
        return _get_version_of_op(candidate_ops, curr_opset_version())

        A utility function that retrieves an op cls using the curr_opset_version
        
coremltools/converters/mil/mil/ops/registry.py