Compatibility with Pydantic >= 2 through pydantic.v1

[SarahG-579462]

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Recently, pygeoapi's pydantic was downgraded from 2.0-compatible to pydantic < 1. This removed compatibility with two of our libraries, xscen and xclim, for climate data processing, due to intake-esm's current requirement on pydantic > 2

Because we require these in the use of our pygeoapi process plugins, this change forced us to use either very outdated versions of xscen (and thus xarray, pandas, xclim, etc.), or a very outdated version of pygeoapi.

Thankfully, a simple fix is available by the use of pydantic 2's backwards-compatible pydantic.v1 module.

It is not entirely clear to me why pydantic was downgraded, the best explanation I can see in the discussion was due to "versionitis".

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Pydantic issues:
#1573
#1341
#1584

[ridoo]

Seems that the dev team has decided to "decouple" more from pydantic in favor of using native dataclass and Protocols (PEP-544). @francbartoli mentioned them in #1547. Not sure how deep this was discussed before, but Protocols has been mentioned before the versionitis term in the last code sprint meeting:

• Protocol / duck typing
  • introduce after api.py refactor in core to allows extensibility
  • do not touch plugins atm
• pydantic
  • master is broke because of versionitis
  • p1 PR to downgrade pydantic 2 --> 1
  • release thereafter
  • should NOT affect rebasing during api refactor

This does not answer your question, why pygeoapi isn't switching to v2 and using pydantic.v1 module. I only can guess, that there are other parts using pydantic which deserve some refactoring first.

@francbartoli @tomkralidis do you have strong arguments not using pydantic anymore? As far I have read things on v2, it got a lot faster. Is this versionitis (sorry for re-calling this term again :)) a temporary issue or do some other problems keep you from resolving this?

[tomkralidis]

Given RFC2, and that our current base OS is Ubuntu jammy, we are bound to OS specific versions. AFAICT, Pydantic is at version 1.8.2 on jammy.

[francbartoli]

@SarahG-579462 @ridoo Pydantic was downgraded to adhere with RFC2 as @tomkralidis mentioned.

Also, the direction of the project is to prefer the simplicity of plain standard dictionaries over the translation from Pydantic models when needed.
However, I recognise the robustness/easiness of a pydantic data validation/serialisation and I'm in the same condition in some downstream projects that I maintain.
That's why I was trying to design a more abstract structure that allows:

• firstly, to remove entirely Pydantic from the code base
• secondly to easily replace, with a consolidated pattern like duck typing, a standard dataclass model with a Pydantic one using a new pygeoapi plugin module that can be eventually declared in the configuration

Hopefully, this might happen soon but most probably after the completion of v2 ubuntu packaging

I Hope this clarifies further.

[ridoo]

@francbartoli thanks for giving more background! BTW, I got notified that #1547 got selected to be closed by github-actions.

[francbartoli]

@ridoo @SarahG-579462 python3-pydantic-core is now available as a package in Debian. Accordingly to RFC2, now I'm going to revert #1584 #1596 and will add the package to the CI docker image (cc @tomkralidis)

[tomkralidis]

Thanks @francbartoli. @kalxas let us know if this works/any issues.

[kalxas]

The package seems to be in Unstable: https://packages.debian.org/sid/python3-pydantic-core

[kalxas]

Lets wait until this ends up in a Debian/Ubuntu stable release