BUG: Remove unnecessary validation to non-string columns/index in df.to_parquet

[mroeschke]

• closes BUG: Unable to write an empty dataframe to parquet #52034 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[phofl]

This might be too broad? An empty Index with int dtype should probably still raise?

E.g. Index([1], dtype="int64") should behave the same as Index([], dtype="int64")?

[mroeschke]

Hmm actually, do you know why we have this limitation on string columns names? pyarrow doesn't seem to have this limitation.

In [25]: tb = pa.Table.from_pandas(pd.DataFrame({1: [2]}))

In [26]: tb
Out[26]:
pyarrow.Table
1: int64
----
1: [[2]]

In [27]: pq.write_table(tb, "abc")

In [28]: pq.read_table("abc")
Out[28]:
pyarrow.Table
1: int64
----
1: [[2]]

[phofl]

This could be an old artefact (same as for read_orc that we removed a couple of days ago), so I'd be ok with getting rid of this if not necessary

[phofl]

thx @mroeschke

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 2.0.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 88f2df5f65e8ff575ee7bdbf2bfa129893573f62

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #52036: BUG: Remove unnecessary validation to non-string columns/index in df.to_parquet'

4. Push to a named branch:

git push YOURFORK 2.0.x:auto-backport-of-pr-52036-on-2.0.x

5. Create a PR against branch 2.0.x, I would have named this PR:

"Backport PR #52036 on branch 2.0.x (BUG: Remove unnecessary validation to non-string columns/index in df.to_parquet)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.