[ONNX] support for setting/getting string onnx tensor shapes (#1478) (#1480)

* [ONNX] support for setting/getting string onnx tensor shapes

* Apply suggestions from code review

Author: bfineran

src/sparseml/onnx/utils/helpers.py

@@ -1216,24 +1216,30 @@ def get_tensor_shape(tensor: onnx.TensorProto) -> List[int]:
     return [dim.dim_value for dim in tensor.type.tensor_type.shape.dim]
 
 
-def get_tensor_dim_shape(tensor: onnx.TensorProto, dim: int) -> int:
+def get_tensor_dim_shape(tensor: onnx.TensorProto, dim: Union[int, str]) -> int:
     """
     :param tensor: ONNX tensor to get the shape of a dimension of
     :param dim: dimension index of the tensor to get the shape of
     :return: shape of the tensor at the given dimension
     """
-    return tensor.type.tensor_type.shape.dim[dim].dim_value
+    return (
+        tensor.type.tensor_type.shape.dim[dim].dim_value
+        or tensor.type.tensor_type.shape.dim[dim].dim_param
+    )
 
 
-def set_tensor_dim_shape(tensor: onnx.TensorProto, dim: int, value: int):
+def set_tensor_dim_shape(tensor: onnx.TensorProto, dim: int, value: Union[int, str]):
     """
     Sets the shape of the tensor at the given dimension to the given value
 
     :param tensor: ONNX tensor to modify the shape of
     :param dim: dimension index of the tensor to modify the shape of
     :param value: new shape for the given dimension
     """
-    tensor.type.tensor_type.shape.dim[dim].dim_value = value
+    if isinstance(value, str):
+        tensor.type.tensor_type.shape.dim[dim].dim_param = value
+    else:
+        tensor.type.tensor_type.shape.dim[dim].dim_value = value
 
 
 def override_model_input_shape(model: Union[str, onnx.ModelProto], shape: List[int]):