class torchrl.modules.tensordict_module.SafeSequential(*args, **kwargs)[source]

A safe sequence of TensorDictModules.

Similarly to nn.Sequence which passes a tensor through a chain of mappings that read and write a single tensor each, this module will read and write over a tensordict by querying each of the input modules. When calling a TensorDictSequencial instance with a functional module, it is expected that the parameter lists (and buffers) will be concatenated in a single list.

  • modules (iterable of TensorDictModules) – ordered sequence of TensorDictModule instances to be run sequentially.

  • 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 True AND if the stack does not have the required keys, then SafeSequential will scan through the sub-tensordicts looking for those that have the required keys, if any.

TensorDictSequence supports functional, modular and vmap coding: .. rubric:: Examples

>>> import torch
>>> from tensordict import TensorDict
>>> from import CompositeSpec, UnboundedContinuousTensorSpec
>>> from torchrl.modules import TanhNormal, SafeSequential, TensorDictModule, NormalParamWrapper
>>> from torchrl.modules.tensordict_module import SafeProbabilisticModule
>>> td = TensorDict({"input": torch.randn(3, 4)}, [3,])
>>> spec1 = CompositeSpec(hidden=UnboundedContinuousTensorSpec(4), loc=None, scale=None)
>>> net1 = NormalParamWrapper(torch.nn.Linear(4, 8))
>>> module1 = TensorDictModule(net1, in_keys=["input"], out_keys=["loc", "scale"])
>>> td_module1 = SafeProbabilisticModule(
...     module=module1,
...     spec=spec1,
...     in_keys=["loc", "scale"],
...     out_keys=["hidden"],
...     distribution_class=TanhNormal,
...     return_log_prob=True,
... )
>>> spec2 = UnboundedContinuousTensorSpec(8)
>>> module2 = torch.nn.Linear(4, 8)
>>> td_module2 = TensorDictModule(
...    module=module2,
...    spec=spec2,
...    in_keys=["hidden"],
...    out_keys=["output"],
...    )
>>> td_module = SafeSequential(td_module1, td_module2)
>>> params = TensorDict.from_module(td_module)
>>> with params.to_module(td_module):
...     td_module(td)
>>> print(td)
        hidden: Tensor(torch.Size([3, 4]), dtype=torch.float32),
        input: Tensor(torch.Size([3, 4]), dtype=torch.float32),
        loc: Tensor(torch.Size([3, 4]), dtype=torch.float32),
        output: Tensor(torch.Size([3, 8]), dtype=torch.float32),
        sample_log_prob: Tensor(torch.Size([3, 1]), dtype=torch.float32),
        scale: Tensor(torch.Size([3, 4]), dtype=torch.float32)},
>>> # The module spec aggregates all the input specs:
>>> print(td_module.spec)
    hidden: UnboundedContinuousTensorSpec(
        shape=torch.Size([4]), space=None, device=cpu, dtype=torch.float32, domain=continuous),
    loc: None,
    scale: None,
    output: UnboundedContinuousTensorSpec(
        shape=torch.Size([8]), space=None, device=cpu, dtype=torch.float32, domain=continuous))
In the vmap case:
>>> from torch import vmap
>>> params = params.expand(4, *params.shape)
>>> td_vmap = vmap(td_module, (None, 0))(td, params)
>>> print(td_vmap)
        hidden: Tensor(torch.Size([4, 3, 4]), dtype=torch.float32),
        input: Tensor(torch.Size([4, 3, 4]), dtype=torch.float32),
        loc: Tensor(torch.Size([4, 3, 4]), dtype=torch.float32),
        output: Tensor(torch.Size([4, 3, 8]), dtype=torch.float32),
        sample_log_prob: Tensor(torch.Size([4, 3, 1]), dtype=torch.float32),
        scale: Tensor(torch.Size([4, 3, 4]), dtype=torch.float32)},
    batch_size=torch.Size([4, 3]),


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