Add pydantic.v1 namespace to Pydantic v1

[exs-dmiketa]

Change Summary

Following jenshnielsen's brilliant idea in #6022, I added a pydantic.v1 alias to the v1 version of Pydantic. This will enable cross-version Pydantic support and easier migration of expansive v1 codebases by switching all pydantic imports to pydantic.v1 and removing the upper bound.

Fix #6022

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist
• Tests pass on CI
• Documentation reflects the changes where applicable
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @hramezani

skip change file check

[exs-dmiketa]

This is my first Pydantic PR so sincere apologies if I'm doing this wrong!

I added a very simple test to capture the main functionality.

Crucially, the following will not work: from pydantic.v1.dataclasses import dataclass. But from pydantic.v1 import dataclasses will. We could try to fool the submodule detection in at least two ways:

1. Copy entire files into a v1 subfolder. (Not massively different from the "v1 in v2" setup.)
2. Put dummy files into a v1 subfolder, e.g. v1/dataclasses.py, and only reimport the top-level corresponding file (from ..dataclasses import *)

Given that this would be merely a transitional solution to help users move from v1 to v2, I'm not sure the issue is critical, but happy to defer to maintainers. Please review. :)

[sydney-runkle]

@exs-dmiketa,

Great, thanks! We'll release this change with an upcoming V1 patch (probably next week).

[exs-dwoodward]

Hi all, this change is useful for things being imported directly like:

from pydantic import ...

but for imports like:

from pydantic.fields import ModelField
from pydantic.generics import GenericModel

or:

from pydantic import fields
from pydantic import generics

it doesn't translate as well. @sydney-runkle would a PR that adds the ability to do these kinds of imports from the v1.py module be useful? IIUC that would make v1 --> v2 migration (with the same existing v1 types / models of course) simply turn into a find + replace of from pydantic --> from pydantic.v1 in all cases. I have a branch locally with this and am happy to contribute a PR if you think it would be useful!