fix(mpl): disconnect toolbar callbacks on cell rerun

[kirangadhave]

Summary

Fixes #9514. FigureCanvasBase.callbacks is a property delegating to figure._canvas_callbacks, so canvases sharing a figure share one event registry. Each mpl.interactive rerun left the old toolbar's _zoom_pan_handler on the registry, causing duplicate dispatch and a second Axes.end_pan to del an already-deleted _pan_start.

The fix disconnects the old toolbar's handlers in _MplCleanupHandle.dispose. Also drops the long-broken canvas.close() (no such method on FigureCanvasWebAgg) and replaces silent excepts with LOGGER.exception.

---

Another issue that surfaced was errors thrown in mpl_interactive bubbles up and kills the kernel, requiring a restart. This would likely apply to any comm callback whose handler can raise. I am tracking a fix for that in separately.

Test plan

• New unit test asserts a single toolbar handler remains on figure._canvas_callbacks after dispose + re-instantiate
• Existing _MplCleanupHandle tests updated to match the new dispose flow
• Manual: 4-step gesture from mpl.interactive raise internal error after move and zoom. #9514 (pan → rerun cell → zoom → pan); kernel survives

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	May 12, 2026 10:08pm

[kirangadhave]

@cubic-dev-ai

[cubic-dev-ai]

@cubic-dev-ai

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[cubic-dev-ai]

No issues found across 2 files

Architecture diagram

sequenceDiagram
    participant Cell as Marimo Cell Runtime
    participant MplUI as mpl_interactive UIElement
    participant Handle as _MplCleanupHandle
    participant Canvas as FigureCanvasWebAgg
    participant Reg as figure._canvas_callbacks
    participant Toolbar as NavigationToolbar2WebAgg
    participant WS as WebSocket

    Note over Cell,WS: Cell rerun lifecycle — shared figure event registry

    Cell->>MplUI: Create (first run)
    MplUI->>Canvas: get canvas
    Canvas->>Reg: callback registry (shared per figure)
    MplUI->>Toolbar: __init__ (register _zoom_pan_handler)
    Toolbar->>Reg: register "button_press_event" handler
    Toolbar->>Reg: register "button_release_event" handler
    MplUI->>WS: open WebSocket

    Note over Cell,WS: Cell rerun — dispose old toolbar, then create new

    Cell->>Handle: dispose()
    Handle->>Canvas: get toolbar reference
    Handle->>Handle: _disconnect_owner_callbacks(canvas, toolbar)
    Handle->>Canvas: access callbacks property
    Canvas->>Reg: return shared registry
    Handle->>Reg: iterate registered handlers
    Handle->>Reg: match handlers owned by old toolbar
    Handle->>Reg: disconnect(cid) for each match
    Reg-->>Handle: handlers removed
    Handle->>WS: remove_web_socket()
    WS-->>Handle: disconnected
    Handle->>Canvas: restore original figure DPI/size
    Handle->>MplUI: close comm

    Cell->>MplUI: Create new instance (rerun)
    MplUI->>Canvas: get canvas (same figure)
    Canvas->>Reg: shared registry (old handlers now removed)
    MplUI->>Toolbar: __init__ (register _zoom_pan_handler)
    Toolbar->>Reg: register "button_press_event" handler
    Toolbar->>Reg: register "button_release_event" handler
    Reg-->>Toolbar: only one handler pair registered

    Note over Cell,Reg: Result: single handler, no duplicate dispatch

    alt Error during disconnect
        Handle->>Handle: catch Exception
        Handle->>Handle: LOGGER.exception(...)
    end

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[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="tests/_plugins/ui/_impl/test_from_mpl_interactive.py">

<violation number="1" location="tests/_plugins/ui/_impl/test_from_mpl_interactive.py:310">
P2: Avoid patching `MagicMock`'s class here; it leaks the failing `callbacks` property into later tests.</violation>
</file>

Architecture diagram

sequenceDiagram
    participant Cell as Marimo Cell Runtime
    participant MplUI as mpl_interactive UIElement
    participant Handle as _MplCleanupHandle
    participant Canvas as FigureCanvasWebAgg
    participant Reg as figure._canvas_callbacks
    participant Toolbar as NavigationToolbar2WebAgg
    participant WS as WebSocket

    Note over Cell,WS: Cell rerun lifecycle — shared figure event registry

    Cell->>MplUI: Create (first run)
    MplUI->>Canvas: get canvas
    Canvas->>Reg: callback registry (shared per figure)
    MplUI->>Toolbar: __init__ (register _zoom_pan_handler)
    Toolbar->>Reg: register "button_press_event" handler
    Toolbar->>Reg: register "button_release_event" handler
    MplUI->>WS: open WebSocket

    Note over Cell,WS: Cell rerun — dispose old toolbar, then create new

    Cell->>Handle: dispose()
    Handle->>Canvas: get toolbar reference
    Handle->>Handle: _disconnect_owner_callbacks(canvas, toolbar)
    Handle->>Canvas: access callbacks property
    Canvas->>Reg: return shared registry
    Handle->>Reg: iterate registered handlers
    Handle->>Reg: match handlers owned by old toolbar
    Handle->>Reg: disconnect(cid) for each match
    Reg-->>Handle: handlers removed
    Handle->>WS: remove_web_socket()
    WS-->>Handle: disconnected
    Handle->>Canvas: restore original figure DPI/size
    Handle->>MplUI: close comm

    Cell->>MplUI: Create new instance (rerun)
    MplUI->>Canvas: get canvas (same figure)
    Canvas->>Reg: shared registry (old handlers now removed)
    MplUI->>Toolbar: __init__ (register _zoom_pan_handler)
    Toolbar->>Reg: register "button_press_event" handler
    Toolbar->>Reg: register "button_release_event" handler
    Reg-->>Toolbar: only one handler pair registered

    Note over Cell,Reg: Result: single handler, no duplicate dispatch

    alt Error during disconnect
        Handle->>Handle: catch Exception
        Handle->>Handle: LOGGER.exception(...)
    end

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[github-actions]

🚀 Development release published. You may be able to view the changes at https://marimo.app?v=0.23.7-dev11