Data interface

Last updated: 05/19/2025 (API docstrings are auto-generated).

DataProto is the interface for data exchange.

The verl.DataProto class contains two key members:

• batch: a tensordict.TensorDict object for the actual data

• meta_info: a Dict with additional meta information

TensorDict

DataProto.batch is built on top of tensordict, a project in the PyTorch ecosystem. A TensorDict is a dict-like container for tensors. To instantiate a TensorDict, you must specify key-value pairs as well as the batch size.

>>> import torch
>>> from tensordict import TensorDict
>>> tensordict = TensorDict({"zeros": torch.zeros(2, 3, 4), "ones": torch.ones(2, 3, 5)}, batch_size=[2,])
>>> tensordict["twos"] = 2 * torch.ones(2, 5, 6)
>>> zeros = tensordict["zeros"]
>>> tensordict
TensorDict(
fields={
    ones: Tensor(shape=torch.Size([2, 3, 5]), device=cpu, dtype=torch.float32, is_shared=False),
    twos: Tensor(shape=torch.Size([2, 5, 6]), device=cpu, dtype=torch.float32, is_shared=False),
    zeros: Tensor(shape=torch.Size([2, 3, 4]), device=cpu, dtype=torch.float32, is_shared=False)},
batch_size=torch.Size([2]),
device=None,
is_shared=False)

One can also index a tensordict along its batch_size. The contents of the TensorDict can be manipulated collectively as well.

>>> tensordict[..., :1]
TensorDict(
fields={
    ones: Tensor(shape=torch.Size([1, 3, 5]), device=cpu, dtype=torch.float32, is_shared=False),
    twos: Tensor(shape=torch.Size([1, 5, 6]), device=cpu, dtype=torch.float32, is_shared=False),
    zeros: Tensor(shape=torch.Size([1, 3, 4]), device=cpu, dtype=torch.float32, is_shared=False)},
batch_size=torch.Size([1]),
device=None,
is_shared=False)
>>> tensordict = tensordict.to("cuda:0")
>>> tensordict = tensordict.reshape(6)

For more about tensordict.TensorDict usage, see the official tensordict documentation.

Core APIs