Don't use astype for torch.Tensor (#2242)

* Broke apart the logic of use_torch and not _process_weights_and_bonds to more clearly read it. Only apply .astype to the np version.

* Add test for weights and bonds using torch.

bittensor/metagraph.py

@@ -25,10 +25,11 @@
 import bittensor
 from os import listdir
 from os.path import join
-from typing import List, Optional, Union, Tuple
+from typing import List, Optional, Union, Tuple, cast
 
 from bittensor.chain_data import AxonInfo
 from bittensor.utils.registration import torch, use_torch
+from bittensor.utils import weight_utils
 
 METAGRAPH_STATE_DICT_NDARRAY_KEYS = [
     "version",
@@ -648,33 +649,40 @@ def _process_weights_or_bonds(
 
                 self.weights = self._process_weights_or_bonds(raw_weights_data, "weights")
         """
-        data_array = []
+        data_array: list[Union[NDArray[np.float32], "torch.Tensor"]] = []
         for item in data:
             if len(item) == 0:
                 if use_torch():
-                    data_array.append(torch.zeros(len(self.neurons)))  # type: ignore
+                    data_array.append(torch.zeros(len(self.neurons)))
                 else:
-                    data_array.append(np.zeros(len(self.neurons), dtype=np.float32))  # type: ignore
+                    data_array.append(np.zeros(len(self.neurons), dtype=np.float32))
             else:
                 uids, values = zip(*item)
                 # TODO: Validate and test the conversion of uids and values to tensor
                 if attribute == "weights":
                     data_array.append(
-                        bittensor.utils.weight_utils.convert_weight_uids_and_vals_to_tensor(
+                        weight_utils.convert_weight_uids_and_vals_to_tensor(
                             len(self.neurons),
                             list(uids),
-                            list(values),  # type: ignore
+                            list(values),
                         )
                     )
                 else:
-                    data_array.append(
-                        bittensor.utils.weight_utils.convert_bond_uids_and_vals_to_tensor(  # type: ignore
-                            len(self.neurons), list(uids), list(values)
-                        ).astype(np.float32)
+                    da_item = weight_utils.convert_bond_uids_and_vals_to_tensor(
+                        len(self.neurons), list(uids), list(values)
                     )
+                    if use_torch():
+                        data_array.append(cast("torch.LongTensor", da_item))
+                    else:
+                        data_array.append(
+                            cast(NDArray[np.float32], da_item).astype(np.float32)
+                        )
         tensor_param: Union["torch.nn.Parameter", NDArray] = (
             (
-                torch.nn.Parameter(torch.stack(data_array), requires_grad=False)
+                torch.nn.Parameter(
+                    torch.stack(cast(list["torch.Tensor"], data_array)),
+                    requires_grad=False,
+                )
                 if len(data_array)
                 else torch.nn.Parameter()
             )
@@ -730,7 +738,7 @@ def _process_root_weights(
                 uids, values = zip(*item)
                 # TODO: Validate and test the conversion of uids and values to tensor
                 data_array.append(
-                    bittensor.utils.weight_utils.convert_root_weight_uids_and_vals_to_tensor(  # type: ignore
+                    weight_utils.convert_root_weight_uids_and_vals_to_tensor(  # type: ignore
                         n_subnets, list(uids), list(values), subnets
                     )
                 )

tests/unit_tests/test_metagraph.py

@@ -124,6 +124,37 @@ def test_process_weights_or_bonds(mock_environment):
     # TODO: Add more checks to ensure the bonds have been processed correctly
 
 
+def test_process_weights_or_bonds_torch(
+    mock_environment, force_legacy_torch_compat_api
+):
+    _, neurons = mock_environment
+    metagraph = bittensor.metagraph(1, sync=False)
+    metagraph.neurons = neurons
+
+    # Test weights processing
+    weights = metagraph._process_weights_or_bonds(
+        data=[neuron.weights for neuron in neurons], attribute="weights"
+    )
+    assert weights.shape[0] == len(
+        neurons
+    )  # Number of rows should be equal to number of neurons
+    assert weights.shape[1] == len(
+        neurons
+    )  # Number of columns should be equal to number of neurons
+    # TODO: Add more checks to ensure the weights have been processed correctly
+
+    # Test bonds processing
+    bonds = metagraph._process_weights_or_bonds(
+        data=[neuron.bonds for neuron in neurons], attribute="bonds"
+    )
+    assert bonds.shape[0] == len(
+        neurons
+    )  # Number of rows should be equal to number of neurons
+    assert bonds.shape[1] == len(
+        neurons
+    )  # Number of columns should be equal to number of neurons
+
+
 # Mocking the bittensor.subtensor class for testing purposes
 @pytest.fixture
 def mock_subtensor():