Fix issue

* Fix issue

* Make string encoding explicit and attributes

src/spox/_utils.py

@@ -56,6 +56,8 @@ def from_array(arr: np.ndarray, name: Optional[str] = None) -> TensorProto:
         data_type=dtype_to_tensor_type(arr.dtype),
         dims=arr.shape,
         # make_tensor fails on scalars. We fix it by calling flatten
-        vals=(arr.astype(bytes) if cast_to_bytes else arr).flatten(),
+        vals=(
+            np.char.encode(arr, encoding="utf-8") if cast_to_bytes else arr
+        ).flatten(),
         raw=False,
     )

tests/test_attr.py

@@ -1,7 +1,7 @@
 import numpy as np
 import pytest
 
-from spox._attributes import AttrTensor
+from spox._attributes import AttrString, AttrStrings, AttrTensor
 
 
 def test_bad_attribute_type_cast_fails(op):
@@ -35,3 +35,8 @@ def test_tensor_does_not_use_raw_data(vals, field, expected):
     assert pb.t.raw_data == b""
     assert getattr(pb.t, field) == expected
     assert pb.t.dims == list(np.array(vals).shape)
+
+
+def test_non_ascii_string_attr():
+    AttrString("🐍")._to_onnx(key="foo")
+    AttrStrings(["🐍"])._to_onnx(key="foo")

tests/test_value_propagation.py

@@ -142,3 +142,7 @@ def test_give_up_silently(op):
         values_int64s=[42],
         default_int64=-1,
     )
+
+
+def test_non_ascii_characters_in_string_tensor(op):
+    op.cast(op.constant(value_string="FööBär"), to=str)