[Breaking Change] MapieRegressor removed in v1.x with no migration guidance

[Tamish03]

[Breaking Change] MapieRegressor removed in v1.x with no migration guidance

Summary

MapieRegressor was removed in MAPIE 1.x without a compatibility shim, deprecation warning, or official migration pathway for users upgrading from MAPIE 0.x tutorials and notebooks.

Any user following pre-1.0 MAPIE examples immediately encounters:

from mapie.regression import MapieRegressor

which now raises:

ImportError: cannot import name 'MapieRegressor'

This creates significant onboarding friction for practitioners migrating from older notebooks, Kaggle examples, blog posts, and StackOverflow solutions.

While debugging this in a Kaggle + Python 3.12 environment, I confirmed that MAPIE 1.x introduced a complete architectural redesign replacing MapieRegressor with specialized conformal regression classes.

Environment

Python: 3.12.x
MAPIE: 1.4.0
scikit-learn: 1.6.1
Environment: Kaggle Notebook / Linux

Steps to Reproduce

pip install mapie
from mapie.regression import MapieRegressor

Expected Behavior

Either:

1. MapieRegressor should exist as a compatibility shim emitting a DeprecationWarning

OR

2. The ImportError should guide users toward the new replacement classes such as:

   • CrossConformalRegressor

   • SplitConformalRegressor

   • ConformalizedQuantileRegressor

OR

3. Official migration documentation should clearly explain:

   • old → new class mappings

   • predict() signature changes

   • alpha → confidence_level migration

Actual Behavior

ImportError: cannot import name 'MapieRegressor' from 'mapie.regression'

No migration guidance or replacement suggestions are provided.

Suggested Fix

Possible improvements:

• Add a lightweight compatibility shim for MapieRegressor

• Raise a custom migration-aware error message

• Add a dedicated 0.x → 1.x migration guide

• Add notebook migration examples for Kaggle/Colab users

Example compatibility guidance:

MAPIE 0.x	MAPIE 1.x
MapieRegressor(method='plus')	CrossConformalRegressor
MapieRegressor(method='base')	SplitConformalRegressor
method='quantile'	ConformalizedQuantileRegressor

I'm also happy to contribute documentation or a migration guide PR if maintainers think it would be useful.

[GBrelurut]

Hello @Tamish03,
Thank you very much for taking the time to detail the issue and to suggest a fix.

However we already have an exhaustive migration guide in the documentation : https://contrib.scikit-learn.org/MAPIE/stable/getting-started/v1-release-notes/#key-changes (see here for the raw file : https://github.com/scikit-learn-contrib/MAPIE/blob/master/doc/getting-started/v1-release-notes.md).
It is already accessible via the index page of the documentation. Plus we wanted to delete this file by the end of next month ( see issue #750 ).

Do you think this satisfactorily solves the issue ? If not, can you tell us how to make the guide more accessible and if we should keep it more than we previously anticipated ?

[Tamish03]

Hello @GBrelurut,

Thank you very much for the clarification and for pointing me to the existing migration guide and release notes.

After reviewing the documentation more carefully, I do agree that the migration information itself is already quite comprehensive. My confusion mainly came from the onboarding/discoverability side rather than missing technical details.

While working in a Kaggle + Python 3.12 environment, I initially encountered:

ImportError: cannot import name 'MapieRegressor'

and my first instinct was to search directly around the import/API transition rather than the release notes section. I suspect newer users following older notebooks/tutorials may experience something similar.

From a beginner/user onboarding perspective, I think a few small discoverability improvements could still help significantly, for example:

• adding a short migration note directly near common regression imports/examples
• adding a visible “Coming from MAPIE 0.x?” pointer in quick-start/install pages
• adding a short note in ImportError troubleshooting guidance
• extending visibility of the v1 migration notes a bit longer before removal

I especially think the current migration guide is valuable for:

• Kaggle users
• notebook-based learners
• users upgrading older tutorials/blog examples
• Python 3.12 environments where users often attempt version downgrades first

So personally, I think keeping the migration guide accessible for a little longer could still reduce onboarding friction for newer users.

Thank you again for the clarification and for maintaining the project. I’d still be happy to help contribute smaller documentation/onboarding improvements if useful.

[GBrelurut]

@Tamish03 Thank you for your feedback. We will see how we can handle the problem as quickly as possible.