Clarifications in docs for data loading

[cgoliver]

The Quickstart and the data handling page have the following example which does not work 'as-is'.

>>> import atom3d.datasets.datasets as da
>>> da.download_dataset('lba', PATH_TO_DATASET) # Download LBA dataset
>>> import atom3d.datasets as da
>>> dataset = da.load_dataset(PATH_TO_DATASET, 'lmdb') # Load LMDB format dataset
>>> print(len(dataset))  # Print length
>>> print(dataset[0].keys()) # Print keys stored in first structure

Some notes:

1. The variable PATH_TO_DATASET cannot have the same value in the download_dataset and the load_dataset calls since the latter requires a path to a subfolder of PATH_TO_DATASET
2. The doc uses SPLIT_NAME without providing a sample value so the user has to guess the options.
3. I would modify this to either set the values of the variables so that the user can copy paste the example directly, or state what values a user should give.

Setting PATH_TO_DATASET='./foo' and running the example as-is results in the following error:

>>> da.download_dataset(
>>> data = da.load_dataset(PATH_TO_DATASET, 'lmdb')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<...>/.venv/lib/python3.9/site-packages/atom3d/datasets/datasets.py", line 426, in load_dataset
    dataset = LMDBDataset(file_list, transform=transform)
  File "<...>/.venv/lib/python3.9/site-packages/atom3d/datasets/datasets.py", line 58, in __init__
    env = lmdb.open(str(self.data_file), max_readers=1, readonly=True,
lmdb.Error: <...>/foo: No such file or directory

---

The second example which was not working is the load_example_dataset also in the Using datasets page.

This is the snippet from the docs:

>>> from atom3d.data.example import load_example_dataset
>>> dataset = load_example_dataset()

Running this produces the following error:

>>> dataset = load_example_dataset()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<...>/venv/lib/python3.9/site-packages/atom3d/data/example.py", line 23, in load_example_dataset
    dataset = da.load_dataset(str(Path(__file__).parent.absolute()) + '/test_lmdb', 'lmdb')
  File "<...>/venv/lib/python3.9/site-packages/atom3d/datasets/datasets.py", line 426, in load_dataset
    dataset = LMDBDataset(file_list, transform=transform)
  File "<...>/.venv/lib/python3.9/site-packages/atom3d/datasets/datasets.py", line 56, in __init__
    raise FileNotFoundError(self.data_file)
FileNotFoundError: <...>/.venv/lib/python3.9/site-packages/atom3d/data/test_lmdb

Version

python: 3.9.13
atom3d: 'v0.2.6'
os: MacOS 10.15.7