[nnx] try casting integers keys in State.replace_by_pure_dict

flax/nnx/statelib.py

@@ -179,11 +179,17 @@ def to_pure_dict(self,
   def replace_by_pure_dict(self,
                            pure_dict: dict[str, tp.Any],
                            replace_fn: SetValueFn | None = None):
+    def try_convert_int(x):
+      try:
+        return int(x)
+      except ValueError:
+        return x
     # Works for nnx.Variable and nnx.VariableState
     if replace_fn is None:
       replace_fn = lambda x, v: x.replace(v) if hasattr(x, 'replace') else v
     current_flat = self.flat_state()
     for kp, v in traversals.flatten_mapping(pure_dict).items():
+      kp = tuple(map(try_convert_int, kp))
       if kp not in current_flat:
         raise ValueError(f'key in pure_dict not available in state: {kp}')
       current_flat[kp] = replace_fn(current_flat[kp], v)

tests/nnx/integration_test.py

@@ -12,12 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import tempfile
 import typing as tp
 
 from absl.testing import absltest
 import jax
 import jax.numpy as jnp
 import numpy as np
+import orbax.checkpoint as ocp
 
 from flax import nnx
 
@@ -259,6 +261,44 @@ def __call__(self, x):
 
     assert 'y' in intermediates
 
+  def test_replace_by_pure_dict(self):
+    class MLPs(nnx.Module):
+      def __init__(self, dim, rngs: nnx.Rngs):
+        self.layers = []
+        for _ in range(4):
+          self.layers.append(nnx.Linear(dim, dim, rngs=rngs, use_bias=False))
+
+      def __call__(self, x):
+        for layer in self.layers:
+          x = layer(x)
+        return x
+
+    model = MLPs(4, rngs=nnx.Rngs(0))
+    x = jax.random.normal(jax.random.key(42), (3, 4))
+    assert model(x).shape == (3, 4)
+
+    _, state = nnx.split(model)
+    pure_dict_state = state.to_pure_dict()
+    nnx.display(pure_dict_state)
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+      ckpt_dir = ocp.test_utils.erase_and_create_empty(
+        tmpdir + '/my-checkpoints/'
+      )
+      checkpointer = ocp.StandardCheckpointer()
+      # checkpointer.save(ckpt_dir / 'state', state)
+      checkpointer.save(ckpt_dir / 'pure_dict', pure_dict_state)
+
+      # Restore as a pure dictionary.
+      restored_pure_dict = checkpointer.restore(ckpt_dir / 'pure_dict')
+      nnx.display(restored_pure_dict)
+
+      abstract_model = nnx.eval_shape(lambda: MLPs(4, rngs=nnx.Rngs(0)))
+      graphdef, abstract_state = nnx.split(abstract_model)
+      abstract_state.replace_by_pure_dict(restored_pure_dict)
+      model = nnx.merge(graphdef, abstract_state)
+      assert model(x).shape == (3, 4)  # The model still works!
+
 
 if __name__ == '__main__':
   absltest.main()