Only-data dataset loaded unexpectedly as validation split
MEMBER
I see two options:
1. drop the "dev" keyword since it can be considered too generic
2. improve the pattern to something more reasonable, e.g. asking for a separator before and after "dev"
```python
["*[ ._-]dev[ ._-]*", "dev[ ._-]*"]
```

I think 2. is nice. If we agree on this one we can even decide to require the separation for the other split keywords "train", "test" etc.
2022-02-25T13:01:36Z
https://github.com/huggingface/datasets/issues/3788#issuecomment-1050833535
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2022-02-25T13:03:33Z
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MEMBER
Yes, I had something like that on mind: "dev" not being part of a word.
```
"[^a-zA-Z]dev[^a-zA-Z]"
2022-02-25T13:04:43Z
https://github.com/huggingface/datasets/issues/3788#issuecomment-1050835924
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2022-02-25T13:12:28Z
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CONTRIBUTOR
Is there a reason why we want that regex? It feels like something that'll still be an issue for some weird case. "my_dataset_dev" doesn't match your regex, "my_dataset_validation" doesn't either ... Why not always "train" unless specified?
2022-02-25T13:06:35Z
https://github.com/huggingface/datasets/issues/3788#issuecomment-1050837333
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2022-02-25T13:07:01Z
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MEMBER
The regex is needed as part of our effort to make datasets configurable without code. In particular we define some generic dataset repository structures that users can follow

> ```
> "[^a-zA-Z]*dev[^a-zA-Z]*"
> ```

unfortunately our glob doesn't support "^": 

https://github.com/fsspec/filesystem_spec/blob/3e739db7e53f5b408319dcc9d11e92bc1f938902/fsspec/spec.py#L465-L479
2022-02-25T13:12:22Z
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2022-02-25T13:12:55Z
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MEMBER
> "my_dataset_dev" doesn't match your regex, "my_dataset_validation" doesn't either ... Why not always "train" unless specified?

And `my_dataset_dev.foo` would match the pattern, and we also have the same pattern but for the "validation" keyword so `my_dataset_validation.foo` would work too
2022-02-25T13:16:47Z
https://github.com/huggingface/datasets/issues/3788#issuecomment-1050845152
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CONTRIBUTOR
> The regex is needed as part of our effort to make datasets configurable without code

This feels like coding with the filename ^^'
2022-02-25T23:42:55Z
https://github.com/huggingface/datasets/issues/3788#issuecomment-1051368699
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2022-02-25T23:43:03Z
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MEMBER
This is still much easier than having to write a full dataset script right ? :p
2022-02-28T11:22:22Z
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## Describe the bug
As reported by @thomasw21 and @lhoestq, a dataset containing only a data file whose name matches the pattern `*dev*` will be returned as VALIDATION split, even if this is not the desired behavior, e.g. a file named `datosdevision.jsonl.gz`.