nlp re-creates already-there caches when using a script, but not within a shell
{'login': 'TevenLeScao', 'id': 26709476, 'node_id': 'MDQ6VXNlcjI2NzA5NDc2', 'avatar_url': 'https://avatars.githubusercontent.com/u/26709476?v=4', 'gravatar_id': '', 'url': 'https://api.github.com/users/TevenLeScao', 'html_url': 'https://github.com/TevenLeScao', 'followers_url': 'https://api.github.com/users/TevenLeScao/followers', 'following_url': 'https://api.github.com/users/TevenLeScao/following{/other_user}', 'gists_url': 'https://api.github.com/users/TevenLeScao/gists{/gist_id}', 'starred_url': 'https://api.github.com/users/TevenLeScao/starred{/owner}{/repo}', 'subscriptions_url': 'https://api.github.com/users/TevenLeScao/subscriptions', 'organizations_url': 'https://api.github.com/users/TevenLeScao/orgs', 'repos_url': 'https://api.github.com/users/TevenLeScao/repos', 'events_url': 'https://api.github.com/users/TevenLeScao/events{/privacy}', 'received_events_url': 'https://api.github.com/users/TevenLeScao/received_events', 'type': 'User', 'site_admin': False}
[]
[]
Couln't reproduce on my side :/ 
let me know if you manage to reproduce on another env (colab for example) Fixed with a clean re-install!
`nlp` keeps creating new caches for the same file when launching `filter` from a script, and behaves correctly from within the shell.

Example: try running

```
import nlp

hans_easy_data = nlp.load_dataset('hans', split="validation").filter(lambda x: x['label'] == 0)
hans_hard_data = nlp.load_dataset('hans', split="validation").filter(lambda x: x['label'] == 1)
```

twice. If launched from a `file.py` script, the cache will be re-created the second time. If launched as 3 shell/`ipython` commands, `nlp` will correctly re-use the cache.
As observed with @lhoestq.
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