Replace onnx.mapping reference with helper

Author: nnpvaan

onnx_tf/common/data_type.py

@@ -1,7 +1,7 @@
 from numbers import Number
 
 import numpy as np
-from onnx import mapping
+from onnx import helper
 from onnx import TensorProto
 import tensorflow as tf
 
@@ -33,8 +33,8 @@ def tf2onnx(dtype):
 
   onnx_dtype = None
   try:
-    onnx_dtype = mapping.NP_TYPE_TO_TENSOR_TYPE[np.dtype(
-        tf_dype.as_numpy_dtype)]
+    onnx_dtype = helper.np_dtype_to_tensor_dtype(np.dtype(
+        tf_dype.as_numpy_dtype))
   finally:
     if onnx_dtype is None:
       common.logger.warning(

onnx_tf/handlers/backend/sequence_empty.py

@@ -4,15 +4,15 @@
 from onnx_tf.handlers.backend_handler import BackendHandler
 from onnx_tf.handlers.handler import onnx_op
 from onnx_tf.common import data_type
-from onnx import mapping
+from onnx import helper
 
 
 @onnx_op("SequenceEmpty")
 class SequenceEmpty(BackendHandler):
 
   @classmethod
   def version_11(cls, node, **kwargs):
-    default_dtype = mapping.NP_TYPE_TO_TENSOR_TYPE[np.dtype('float32')]
+    default_dtype = helper.np_dtype_to_tensor_dtype(np.dtype('float32'))
     dtype = data_type.onnx2tf(node.attrs.get("dtype", default_dtype))
 
     ragged = tf.RaggedTensor.from_row_lengths(values=[], row_lengths=[])