DOC default random_state in _fetch_20newsgroup is 42, not None

[mathurinm]

See : https://github.com/scikit-learn/scikit-learn/blob/main/sklearn/datasets/_twenty_newsgroups.py#L173

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[betatim]

Should we make the fix in the other direction (change the code, keep the docs)? It seems odd to use 42 as default, the rest of scikit-learn uses None.

[mathurinm]

Changing the default to None seems more in line with the rest of the codebase but it would require a deprecation cycle, as it will change the behaviour of existing code, right?

[betatim]

I'd consider it a bug fix, and for those I don't think we need a deprecation cycle.

[jeremiedbb]

Most dataset fetchers that have a random_state have it None by default. Only this one and fetch_olivetti_faces have a non None default, and fetch_olivetti_faces is correctly documented. I'd like to have None by default consistently in all fetchers at some point. For now I'm fine with fixing the doc. Thanks @mathurinm