[Feature] inplace arg for TensorDictSequential

ghstack-source-id: 3f392cb
Pull Request resolved: #1253

Author: Vincent Moens

tensordict/nn/sequence.py

@@ -11,6 +11,7 @@
 from typing import Any, Callable, Iterable, List, OrderedDict, overload
 
 from tensordict._nestedkey import NestedKey
+from tensordict._td import TensorDict
 
 from tensordict.nn.common import (
     dispatch,
@@ -61,14 +62,17 @@ class TensorDictSequential(TensorDictModule):
             Regular ``dict`` inputs will be converted to ``OrderedDict`` if necessary.
 
     Keyword Args:
-         partial_tolerant (bool, optional): if True, the input tensordict can miss some of the input keys.
+        partial_tolerant (bool, optional): if True, the input tensordict can miss some of the input keys.
             If so, the only module that will be executed are those who can be executed given the keys that
             are present.
             Also, if the input tensordict is a lazy stack of tensordicts AND if partial_tolerant is :obj:`True` AND if the
             stack does not have the required keys, then TensorDictSequential will scan through the sub-tensordicts
             looking for those that have the required keys, if any. Defaults to False.
-         selected_out_keys (iterable of NestedKeys, optional): the list of out-keys to select. If not provided, all
+        selected_out_keys (iterable of NestedKeys, optional): the list of out-keys to select. If not provided, all
             ``out_keys`` will be written.
+        inplace (bool, optional): if `True`, the input tensordict is modified in-place. If `False`, a new empty
+            :class:`~tensordict.TensorDict` instance is created. If `"empty"`, `input.empty()` is used instead (ie, the
+            output preserves type, device and batch-size). Defaults to `None` (relies on sub-modules).
 
     .. note::
         A :class:`TensorDictSequential` instance may have a long list of output keys, and one may wish to remove
@@ -185,6 +189,7 @@ def __init__(
         *,
         partial_tolerant: bool = False,
         selected_out_keys: List[NestedKey] | None = None,
+        inplace: bool | None = None,
     ) -> None: ...
 
     @overload
@@ -194,13 +199,15 @@ def __init__(
         *,
         partial_tolerant: bool = False,
         selected_out_keys: List[NestedKey] | None = None,
+        inplace: bool | None = None,
     ) -> None: ...
 
     def __init__(
         self,
         *modules: Callable[[TensorDictBase], TensorDictBase],
         partial_tolerant: bool = False,
         selected_out_keys: List[NestedKey] | None = None,
+        inplace: bool | None = None,
     ) -> None:
 
         if len(modules) == 1 and isinstance(modules[0], collections.OrderedDict):
@@ -236,6 +243,7 @@ def __init__(
                 module=nn.ModuleList(list(modules)), in_keys=in_keys, out_keys=out_keys
             )
 
+        self.inplace = inplace
         self.partial_tolerant = partial_tolerant
         if selected_out_keys:
             self._select_before_return = True
@@ -452,6 +460,43 @@ def select_subsequence(
                 in_keys=['b'],
                 out_keys=['d', 'e'])
 
+        The `inplace` argument allows for a fine-grained control over the output type, allowing for instance to write
+        the result of the computational graph in the input object without tracking the intermediate tensors.
+
+        Example:
+            >>> import torch
+            >>> from tensordict import TensorClass
+            >>> from tensordict.nn import TensorDictModule as Mod, TensorDictSequential as Seq
+            >>>
+            >>> class MyClass(TensorClass):
+            ...     input: torch.Tensor
+            ...     output: torch.Tensor | None = None
+            >>>
+            >>> obj = MyClass(torch.randn(2, 3), batch_size=(2,))
+            >>>
+            >>> model = Seq(
+            ...     Mod(
+            ...         lambda x: (x + 1, x - 1),
+            ...         in_keys=["input"],
+            ...         out_keys=[("intermediate", "0"), ("intermediate", "1")],
+            ...         inplace=False
+            ...         ),
+            ...     Mod(
+            ...         lambda y0, y1: y0 * y1,
+            ...         in_keys=[("intermediate", "0"), ("intermediate", "1")],
+            ...         out_keys=["output"],
+            ...         inplace=False
+            ...         ),
+            ...     inplace=True, )
+            >>> print(model(obj))
+            MyClass(
+                input=Tensor(shape=torch.Size([2, 3]), device=cpu, dtype=torch.float32, is_shared=False),
+                output=Tensor(shape=torch.Size([2, 3]), device=cpu, dtype=torch.float32, is_shared=False),
+                output=None,
+                batch_size=torch.Size([2]),
+                device=None,
+                is_shared=False)
+
         """
         if in_keys is None:
             in_keys = deepcopy(self.in_keys)
@@ -558,6 +603,14 @@ def forward(
             tensordict_exec = tensordict.copy()
         else:
             tensordict_exec = tensordict
+        if tensordict_out is None:
+            if self.inplace is True:
+                tensordict_out = tensordict
+            elif self.inplace is False:
+                tensordict_out = TensorDict()
+            elif self.inplace == "empty":
+                tensordict_out = tensordict.empty()
+
         if not len(kwargs):
             for module in self._module_iter():
                 try:

tensordict/tensorclass.py

@@ -1939,7 +1939,8 @@ def _from_dict(
         # We don't want to enforce them to be tensorclasses so we can't do much about it...
         return cls.from_tensordict(
             tensordict=TensorDict(
-                batch_size=batch_size, device=device, batch_dims=batch_dims
+                batch_size=batch_size,
+                device=device,
             ),
             non_tensordict=input_dict,
         )

test/test_nn.py

@@ -1009,6 +1009,41 @@ def test_tdmodule_inplace(self):
 
 
 class TestTDSequence:
+    @pytest.mark.parametrize("inplace", [True, False, None])
+    @pytest.mark.parametrize("module_inplace", [True, False])
+    def test_tdseq_inplace(self, inplace, module_inplace):
+        model = TensorDictSequential(
+            TensorDictModule(
+                lambda x: (x + 1, x - 1),
+                in_keys=["input"],
+                out_keys=[("intermediate", "0"), ("intermediate", "1")],
+                inplace=module_inplace,
+            ),
+            TensorDictModule(
+                lambda y0, y1: y0 * y1,
+                in_keys=[("intermediate", "0"), ("intermediate", "1")],
+                out_keys=["output"],
+                inplace=module_inplace,
+            ),
+            inplace=inplace,
+        )
+        input = TensorDict(input=torch.zeros(()))
+        output = model(input)
+        if inplace:
+            assert output is input
+            assert "input" in output
+        else:
+            if not module_inplace or inplace is False:
+                # In this case, inplace=False and inplace=None have the same behavior
+                assert output is not input, (module_inplace, inplace)
+                assert "input" not in output, (module_inplace, inplace)
+            else:
+                # In this case, inplace=False and inplace=None have the same behavior
+                assert output is input, (module_inplace, inplace)
+                assert "input" in output, (module_inplace, inplace)
+
+        assert "output" in output
+
     def test_ordered_dict(self):
         linear = nn.Linear(3, 4)
         linear.weight.data.fill_(0)