Avoid double formatting in mo.output.replace#9909
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mscolnick merged 1 commit intoJun 29, 2026
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mscolnick
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Rebased this on current Local checks: uv run --group test pytest tests/_runtime/output/test_output.py tests/_server/api/test_auth.py -q
uv run --group dev ruff check marimo/_runtime/output/_output.py tests/_runtime/output/test_output.py tests/_server/api/test_auth.pyThe PR diff is still limited to the output replacement fix and its regression test. |
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Pull request overview
Reduces the cost of mo.output.replace(value) by avoiding a second formatting pass when broadcasting the updated cell output, targeting expensive _repr_html_ / __panel__ formatting paths.
Changes:
- Reuse a single formatted
Htmlobject inmo.output.replaceto prevent duplicate formatter invocation. - Add a regression test that verifies
_repr_html_is only called once duringmo.output.replace.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
marimo/_runtime/output/_output.py |
Changes replace() to reuse the formatted output when emitting the output notification. |
tests/_runtime/output/test_output.py |
Adds a probe-based regression test to ensure formatting only occurs once. |
Comment on lines
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| if value is not None: | ||
| output.append(formatting.as_html(value)) | ||
| write_internal(cell_id=ctx.execution_context.cell_id, value=value) | ||
| html = formatting.as_html(value) | ||
| output.append(html) | ||
| write_internal(cell_id=ctx.execution_context.cell_id, value=html) | ||
| else: | ||
| write_internal(cell_id=ctx.execution_context.cell_id, value=value) |
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Summary
Closes #9681
mo.output.replace(value)was formattingvalueonce for the imperative output list and then again when broadcasting the cell output. This reuses theHtmlobject produced for the output list when sending the notification, so expensive_repr_html_/__panel__paths only run once.A regression test covers a probe object whose
_repr_html_increments a counter.Tests
python -m pytest tests\_runtime\output\test_output.py -qpython -m ruff check marimo\_runtime\output\_output.py tests\_runtime\output\test_output.pygit diff --check