ENH: update html parameter display to match scikit-learn style

[AnimeshPatra2005]

Reference Issues/PRs

Closes #503. Related to sktime/sktime#9497.

What does this implement/fix? Explain your changes.

scikit-learn has updated how they display parameters in the HTML representation of estimators. This PR updates scikit-base to match.

Previously, clicking an estimator box in a Jupyter notebook showed a raw <pre> string like MyEstimator(alpha=0.5).

This PR replaces that with a structured two-column parameter table built from get_params(deep=False), showing each parameter name and its current value in a cleaner, more readable format.

Changes:

• New _params_to_html_table() helper that generates the table HTML
• _write_label_html() gains an optional estimator parameter; when provided, renders the table instead of the pre block
• _write_base_object_html() passes the estimator through
• CSS styles for the table appended to _STYLE

Does your contribution introduce a new dependency? If yes, which one?

No.

What should a reviewer concentrate their feedback on?

• The CSS styling choices for the parameter table
• Whether the fallback to <pre> for non-estimator objects is correct

Any other comments?

Marked as Draft, happy to add unit tests once the approach is confirmed as the right direction.

How it looks like:

[mateuszkasprowicz]

hey @AnimeshPatra2005, this is a solid start!

I created a simple comparison between sklearn 1.8+ and your PR handling of params display:

skbase

single estimator

Code

class SkbaseDemo(BaseEstimator):
    """Tiny estimator for HTML repr smoke tests."""

    def __init__(self, foo=1, bar="hello", multiplier=0.5):
        self.foo = foo
        self.bar = bar
        self.multiplier = multiplier
        super().__init__()


display(SkbaseDemo(foo=42, bar="notebook", multiplier=2.0))

skbase

composite estimator

Code

class SkbaseComponent(BaseObject):
    def __init__(self, a=1, flag=True):
        self.a = a
        self.flag = flag
        super().__init__()


class DemoMeta(BaseMetaObject):
    def __init__(self, steps=None):
        self.steps = steps
        super().__init__()


composite = DemoMeta(
    steps=[
        ("first", SkbaseComponent(a=10, flag=False)),
        ("second", SkbaseComponent(a=99, flag=True)),
    ]
)
display(composite)

sklearn

single estimator

Code

from sklearn.linear_model import LogisticRegression

display(
    LogisticRegression(
        C=0.5, max_iter=200, solver="liblinear", random_state=0
    )
)

sklearn

composite estimator

Code

from sklearn.pipeline import Pipeline
from sklearn.preprocessing import StandardScaler

display(
    Pipeline(
        [
            ("scale", StandardScaler(with_mean=False)),
            ("clf", LogisticRegression(C=2.0, max_iter=500)),
        ]
    )
)

Overview of what's missing

• Separate “Parameters” collapsible - sklearn: class row stays clean, then an inner Parameters section toggles the table;
• Per-parameter documentation on hover - sklearn: dashed-underline names + tooltip text from the docstring.
• Copy parameter name (or name/value) to clipboard - sklearn: small copy control per row;
• See which params differ from defaults - sklearn: emphasizes changed params (e.g. orange); skbase: no default vs user-set distinction.
• Readable values for large/nested objects - sklearn shortens repr (reprlib-style); skbase uses full repr(value) in HTML - can freeze or clutter the cell.
• And of course a small test to ensure we have sk-params-table in the HTML

Where to look in sklearn code

(courtesy of Codex)

sklearn/utils/_repr_html/estimator.py — estimator tree / overall HTML repr
sklearn/utils/_repr_html/params.py — parameter table HTML (ParamsDict, _params_html_repr, etc.)
sklearn/utils/_repr_html/common.py — helpers (e.g. doc links, docstring snippets for params)
sklearn/utils/_repr_html/base.py — ReprHTMLMixin and shared HTML bits
sklearn/utils/_repr_html/estimator.css — layout / estimator chrome
sklearn/utils/_repr_html/params.css — parameter table styling
sklearn/utils/_repr_html/__init__.py — package exports
sklearn/utils/_repr_html/tests/ — tests for the above