fix: handle list-type tooltip encoding in altair chart (#9167)

[mscolnick]

_has_binning() and _get_binned_fields() iterated over
spec["encoding"].values() and called dict methods (.get(), in) on
each value. When tooltip is defined as a list of multiple tooltips,
the encoding value is a list instead of a dict, causing
AttributeError: 'list' object has no attribute 'get'.

Skip list-type encoding values (like tooltip arrays) since they cannot
contain binning configuration.

Closes #9167

[vercel]

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Apr 13, 2026 8:16pm

[Copilot]

Pull request overview

Fixes a crash in mo.ui.altair_chart when Vega-Lite encodings include list-valued channels (notably tooltip=[...]), by preventing _has_binning() / _get_binned_fields() from calling dict methods on list objects.

Changes:

• Skip list-valued entries when scanning spec["encoding"] for binning metadata.
• Add regression tests covering tooltip-as-list behavior for _get_binned_fields(), _has_binning(), and a smoke test for altair_chart(...).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
marimo/_plugins/ui/_impl/altair_chart.py	Avoids AttributeError by skipping list-valued encoding channels during binning detection.
tests/_plugins/ui/_impl/test_altair_chart.py	Adds tests to ensure tooltip lists don’t crash binning detection or altair_chart.

Comments suppressed due to low confidence (1)

marimo/_plugins/ui/_impl/altair_chart.py:96

• _get_binned_fields() currently continues on list-valued encoding channels. This avoids the tooltip crash, but it also drops any binned field definitions contained inside arrays (valid for channels like tooltip/detail/order). That can lead to incorrect binned_fields, and downstream selection filtering may treat binned selections as non-binned. Consider walking list items and extracting bin from any dict elements rather than skipping the whole list.

    for encoding in spec["encoding"].values():
        if isinstance(encoding, list):
            continue
        if encoding.get("bin"):
            # Get the field name
            field = encoding.get("field")
            if field:
                binned_fields[field] = encoding["bin"]

[kirangadhave]

🚀