Enabling array API dispatch causes pipelines to reject dataframe inputs #32836
Description
Describe the bug
Enabling the array API dispatch has a negative side effect on code that usually accepts non-array inputs such as pandas dataframes:
Steps/Code to Reproduce
# %%
import os
os.environ["SCIPY_ARRAY_API"] = "1"
# %%
import sklearn
from sklearn.datasets import fetch_openml
from sklearn.preprocessing import OneHotEncoder
adult = fetch_openml(name="adult", version=2, as_frame=True)
X, y = adult.data, adult.target
with sklearn.config_context(array_api_dispatch=True):
OneHotEncoder().fit(
X.select_dtypes(include=["category", "object"])
)Expected Results
The enabling of array API should not affect the estimator behavior on dataframe inputs.
Actual Results
Traceback (most recent call last):
Cell In[11], [line 11](vscode-notebook-cell:?execution_count=11&line=11)
OneHotEncoder().fit(
File ~/code/scikit-learn/sklearn/base.py:1336 in wrapper
return fit_method(estimator, *args, **kwargs)
File ~/code/scikit-learn/sklearn/preprocessing/_encoders.py:999 in fit
self._fit(
File ~/code/scikit-learn/sklearn/preprocessing/_encoders.py:86 in _fit
X_list, n_samples, n_features = self._check_X(
File ~/code/scikit-learn/sklearn/preprocessing/_encoders.py:69 in _check_X
Xi = check_array(
File ~/code/scikit-learn/sklearn/utils/validation.py:858 in check_array
xp, is_array_api_compliant = get_namespace(array)
File ~/code/scikit-learn/sklearn/utils/_array_api.py:404 in get_namespace
namespace, is_array_api_compliant = array_api_compat.get_namespace(*arrays), True
File ~/code/scikit-learn/sklearn/externals/array_api_compat/common/_helpers.py:643 in array_namespace
raise TypeError(f"{type(x).__name__} is not a supported array type")
TypeError: Series is not a supported array typeVersions
System:
python: 3.13.7 | packaged by conda-forge | (main, Sep 3 2025, 14:24:46) [Clang 19.1.7 ]
executable: /Users/ogrisel/miniforge3/envs/dev/bin/python
machine: macOS-15.6.1-arm64-arm-64bit-Mach-O
Python dependencies:
sklearn: 1.9.dev0
pip: 25.2
setuptools: 80.9.0
numpy: 2.3.3
scipy: 1.16.3
Cython: 3.1.4
pandas: 3.0.0.dev0+2566.g2bb3fef887
matplotlib: 3.10.6
joblib: 1.5.2
threadpoolctl: 3.6.0
Built with OpenMP: True
threadpoolctl info:
user_api: blas
internal_api: openblas
num_threads: 10
prefix: libopenblas
filepath: /Users/ogrisel/miniforge3/envs/dev/lib/libopenblas.0.dylib
version: 0.3.30
threading_layer: openmp
architecture: VORTEX
user_api: openmp
internal_api: openmp
num_threads: 10
prefix: libomp
filepath: /Users/ogrisel/miniforge3/envs/dev/lib/libomp.dylib
version: None