[BUG] - "NameError: name 'gc' is not defined" in "Using Replay Buffers" tutorial

[BrikeX]

In the section "Storing trajectories", an error is reported in the following code

from torchrl.data import SliceSampler

rb = TensorDictReplayBuffer(
    storage=LazyTensorStorage(size),
    sampler=SliceSampler(traj_key="episode", num_slices=4),
    batch_size=8,
)
episode = [torch.zeros](https://pytorch.org/docs/stable/generated/torch.zeros.html#torch.zeros)(10, dtype=torch.int)
episode[:3] = 1
episode[3:5] = 2
episode[5:7] = 3
episode[7:] = 4
steps = [torch.cat](https://pytorch.org/docs/stable/generated/torch.cat.html#torch.cat)([[torch.arange](https://pytorch.org/docs/stable/generated/torch.arange.html#torch.arange)(3), [torch.arange](https://pytorch.org/docs/stable/generated/torch.arange.html#torch.arange)(2), [torch.arange](https://pytorch.org/docs/stable/generated/torch.arange.html#torch.arange)(2), [torch.arange](https://pytorch.org/docs/stable/generated/torch.arange.html#torch.arange)(3)])
data = TensorDict(
    {
        "episode": episode,
        "obs": [torch.randn](https://pytorch.org/docs/stable/generated/torch.randn.html#torch.randn)((3, 4, 5)).expand(10, 3, 4, 5),
        "act": [torch.randn](https://pytorch.org/docs/stable/generated/torch.randn.html#torch.randn)((20,)).expand(10, 20),
        "other": [torch.randn](https://pytorch.org/docs/stable/generated/torch.randn.html#torch.randn)((20, 50)).expand(10, 20, 50),
        "steps": steps,
    },
    [10],
)
rb.extend(data)
sample = rb.sample()
print("episode are grouped", sample["episode"])
print("steps are successive", sample["steps"])

gc.collect()

as

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Cell In[44], line 29
     26 print("episode are grouped", sample["episode"])
     27 print("steps are successive", sample["steps"])
---> 29 gc.collect()

NameError: name 'gc' is not defined

cc @vmoens @nairbv

[svekars]

Can you please provide a link to the tutorial

[vmoens]

I think it's in torchrl
https://github.com/pytorch/rl/blob/619fec69c33966fc92cbb4527d6dad567e094752/tutorials/sphinx-tutorials/rb_tutorial.py#L794
Let's move the discussion there @BrikeX if you don't mind!

[BrikeX]

Can you please provide a link to the tutorial

https://pytorch.org/rl/stable/tutorials/rb_tutorial.html#a-more-complex-examples-using-catframes