DOC Add notes in OrdinalEncoder regardin Python version
closes
@@ -1131,6 +1131,13 @@ class OrdinalEncoder(OneToOneFeatureMixin, _BaseEncoder):
LabelEncoder : Encodes target labels with values between 0 and
``n_classes-1``.
+ Notes
+ -----
+ With a high proportion of `nan` values, inferring categories becomes slow with
+ Python versions before 3.10. The handling of `nan` values was improved
+ from Python 3.10 onwards, (c.f.
+ `bpo-43475 <https://github.com/python/cpython/issues/87641>`_).
+
Examples
--------
Given a dataset with two features, we let the encoder find the unique
