Fix accidental requirement of Pandas 1.5. Bump minimum Pandas version to 0.25. Run tests with it

[binste]

This import introduced in #3114 is not available in Pandas < 1.5 and Altair currently supports Pandas >= 0.18. This PR adds a test run with the lowest supported Pandas version.

@jonmmease Do you know of a good way to make that type check independent of the pandas import? Else, we could fall back on not type-hinting it if necessary. Feel free to push directly to this branch if you have an idea and want to try it out in the GitHub actions workflow.

Pandas 0.18 is from 2016 and we could for sure consider bumping it but I don't think we can go to Pandas 1.5 just yet. Especially not in a minor release of Altair.

[jonmmease]

Ahh, thanks for flagging this @binste, and for working on testing with older pandas.

I'll look into alternatives for the type signature, it might be enough to wrap the import in typing.TYPE_CHECKING, although maybe the mypy tests would fail with the older version of pandas in this case.

In terms of pandas versions, I personally think we could bump the pandas requirement up to 1.0 (released 3.5 years ago) in an Altair minor version, but I agree that 1.5 (released less than 1 year ago) would be too aggressive.

[jonmmease]

huh, looks like the if condition in the GitHub actions isn't working

[jonmmease]

I'm really stumped as to why GitHub actions is always evaluating the "Maybe uninstall optional dependencies" and "Maybe install lowest supported Pandas version" jobs, ignoring the if: conditions (or always evaluating them to true).

[binste]

I think I had the same issue recently over in #3118. I'll give it a try.

[binste]

Seems like you're trying it already. In #3118 I got it working for jsonschema with this line https://github.com/altair-viz/altair/pull/3118/files#diff-5c3fa597431eda03ac3339ae6bf7f05e1a50d6fc7333679ec38e21b337cb6721R32

[jonmmease]

I'll try that again (I think again 😄 )

[jonmmease]

Oh, looks like I needed single quotes. The issue now is with installing pandas 0.18.0 in Python 3.8:

Run pip install pandas==0.18
Collecting pandas==0.18
  Downloading pandas-0.18.0.tar.gz (7.1 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 7.1/7.1 MB 24.2 MB/s eta 0:00:00
  Installing build dependencies: started
  Installing build dependencies: finished with status 'done'
  Getting requirements to build wheel: started
  Getting requirements to build wheel: finished with status 'done'
  Installing backend dependencies: started
  Installing backend dependencies: finished with status 'done'
  Preparing metadata (pyproject.toml): started
  Preparing metadata (pyproject.toml): finished with status 'error'
  error: subprocess-exited-with-error
  
  × Preparing metadata (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> [4 lines of output]
      <string>:39: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
      error in pandas setup command: 'install_requires' must be a string or list of strings containing valid project/version requirement specifiers; Expected end or semicolon (after version specifier)
          pytz >= 20[11](https://github.com/altair-viz/altair/actions/runs/5716874306/job/15489393829?pr=3130#step:6:12)k
               ~~~~~~~^
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

Looks like pandas 0.18.1 didn't ship wheels for Python 3.8. I'll check what the oldest version of pandas is that includes wheels for 3.8 is.

[jonmmease]

The oldest version of pandas with 3.8 wheels is 0.25.3, released 2019-11-01.

I'm personally inclined to update our min supported pandas version to this one for Altair 5.1 so that we don't need to build pandas wheels from source on CI.

[binste]

Thanks for figuring out to use single quotes, weird...

Bumping to minimum version 0.25.3 sounds very reasonable to me too. We can rename this PR and do it all in here. I think there is some code logic somewhere which is for Pandas 0.18. I'll try to find and remove that one too while we're at it.

I can offer to do the Pandas bump and cleanup later this week if you prefer to focus on the issue with the type hint.

[jonmmease]

Sounds good. I'll take this PR and update the min pandas and numpy versions and fix the type hint issue (I'll need to update these versions to get CI working). I won't look for any pandas/numpy compatibility code that could be removed, so if you could do a pass on that at some point that would be great!

[jonmmease]

I think this is ready now @binste, thanks for raising the issues!

[binste]

Great, I removed some part of the code which is now redundant and clarified another one which we need to keep but for other reasons compared to why it was originally implemented.

@jonmmease Could you do a review of my last commits? Feel free to merge afterwards. Thanks!

[jonmmease]

Looks good. Thanks!

[jonmmease]

🎉