Allow passing `desc` to `tqdm` in `Dataset.map()`
{'login': 'cccntu', 'id': 31893406, 'node_id': 'MDQ6VXNlcjMxODkzNDA2', 'avatar_url': 'https://avatars.githubusercontent.com/u/31893406?v=4', 'gravatar_id': '', 'url': 'https://api.github.com/users/cccntu', 'html_url': 'https://github.com/cccntu', 'followers_url': 'https://api.github.com/users/cccntu/followers', 'following_url': 'https://api.github.com/users/cccntu/following{/other_user}', 'gists_url': 'https://api.github.com/users/cccntu/gists{/gist_id}', 'starred_url': 'https://api.github.com/users/cccntu/starred{/owner}{/repo}', 'subscriptions_url': 'https://api.github.com/users/cccntu/subscriptions', 'organizations_url': 'https://api.github.com/users/cccntu/orgs', 'repos_url': 'https://api.github.com/users/cccntu/repos', 'events_url': 'https://api.github.com/users/cccntu/events{/privacy}', 'received_events_url': 'https://api.github.com/users/cccntu/received_events', 'type': 'User', 'site_admin': False}
[{'id': 1935892871, 'node_id': 'MDU6TGFiZWwxOTM1ODkyODcx', 'url': 'https://api.github.com/repos/huggingface/datasets/labels/enhancement', 'name': 'enhancement', 'color': 'a2eeef', 'default': True, 'description': 'New feature or request'}, {'id': 1935892877, 'node_id': 'MDU6TGFiZWwxOTM1ODkyODc3', 'url': 'https://api.github.com/repos/huggingface/datasets/labels/good%20first%20issue', 'name': 'good first issue', 'color': '7057ff', 'default': True, 'description': 'Good for newcomers'}]
[]
Hi @lhoestq,
Should we change `desc` in [pbar](https://github.com/huggingface/datasets/blob/81fcf88172ed5e3026ef68aed4c0ec6980372333/src/datasets/arrow_dataset.py#L1860) to something meaningful? I think the user could pass the `desc` parameter to `map` so that it can be displayed in the tqdm progress bar, as suggested by @cccntu.

When there's no multiprocessing, the `desc` of the progress bar could be the `desc` passed by the user.
In multiprocessing, we were already using a `desc` equal to `"#" + str(rank)`.
We can change it to be `(desc or "") + "#" + str(rank)` instead.

In the end, since both `desc` and `rank` could be None, we can have:
```python
pbar_desc = (desc or "") + "#" + str(rank) if rank is not None else desc
```

Finally let's remember that if we add `desc` as a new parameter to `map`, we should add it to the `ignore_kwargs` list of the `@fingerprint_transform` decorator of `Dataset._map_single` since we don't want this parameter to affect the fingerprint of the resulting dataset.
It's normal to have many `map()` calls, and some of them can take a few minutes,
it would be nice to have a description on the progress bar.

Alternative solution:
Print the description before/after the `map()` call.
{'url': 'https://api.github.com/repos/huggingface/datasets/issues/2330/reactions', 'total_count': 1, '+1': 0, '-1': 0, 'laugh': 0, 'hooray': 0, 'confused': 0, 'heart': 1, 'rocket': 0, 'eyes': 0}