Generate dedicated Python session event types by stephentoub · Pull Request #1063 · github/copilot-sdk

stephentoub · 2026-04-11T18:51:25Z

Summary

Python session events still used quicktype and collapsed payload members into one merged Data model, unlike the newer Go implementation. That made the language bindings inconsistent and increased the chance of naming conflicts as the runtime schema grows.

This change switches Python session-event generation to dedicated per-event payload dataclasses, matching the newer Go-style approach. SessionEvent.from_dict() now dispatches to typed payload classes, unknown events still round-trip through RawSessionEventData, and the Python runtime/tests were updated to handle the typed payload union.

The one non-obvious part is compatibility: the generator also restores legacy top-level helper exports and keeps arbitrary nested mappings in the Data shim as plain dicts so older callers do not break while the generated model becomes more structured.

Validation

python -m pytest test_event_forward_compatibility.py test_commands_and_elicitation.py
python -m pytest --ignore=e2e

scripts/codegen/python.ts

Copilot

Pull request overview

This PR updates the Python SDK’s session-events generation to emit dedicated per-event payload dataclasses (instead of a single merged Data payload), and updates the Python runtime/tests to consume these typed payloads while retaining compatibility shims.

Changes:

Replaced Python session-events quicktype generation with a custom generator that emits per-event payload dataclasses and dispatches in SessionEvent.from_dict().
Updated Python session handling and tests to use typed payload classes (e.g., CommandExecuteData, ElicitationRequestedData) and validate legacy top-level exports + Data shim behavior.
Preserved forward compatibility for unknown event types via SessionEventType.UNKNOWN + RawSessionEventData, plus added several legacy helper aliases.

Show a summary per file

File	Description
scripts/codegen/python.ts	Implements custom Python session-events codegen emitting per-event payload dataclasses, compatibility shims, and typed dispatch.
python/test_event_forward_compatibility.py	Extends forward-compat tests to cover legacy helper exports and `Data` shim dict-preservation behavior.
python/test_commands_and_elicitation.py	Updates tests to construct typed event payloads instead of using the legacy `Data` container.
python/copilot/session.py	Updates broadcast event handling to cast `event.data` to the appropriate generated payload dataclass before accessing fields.

Copilot's findings

Files reviewed: 4/5 changed files
Comments generated: 2

scripts/codegen/python.ts

github-actions

Generated by SDK Consistency Review Agent for issue #1063 · ● 488.3K

python/copilot/session.py

SteveSandersonMS

Generally looks good to me, would be interesting to run it by @brettcannon if you want more authoritative Python feedback.

python/copilot/session.py

Align Python session event generation with the newer Go-style dedicated per-event payload model instead of the old merged quicktype Data shape. This updates the runtime/tests for typed payloads while preserving compatibility aliases and legacy Data behavior for existing callers. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Fix the generated Python docstring escaping that CodeQL flagged, correct dotted-key normalization in the Data compatibility shim, update the stale Go local-cli docs snippet for the newer typed event API, and apply the Python formatter change required by CI. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Normalize trailing whitespace in pyDocstringLiteral to prevent cross-platform codegen drift, and reformat test file with Prettier. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions

Generated by SDK Consistency Review Agent for issue #1063 · ● 687K

- Regenerate session_events.py to match latest schema (removes session.import_legacy, adds reasoning_tokens to AssistantUsageData) - Update docs/setup/local-cli.md Python example to use match-based type narrowing with None check, consistent with python/README.md Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-04-14T15:23:09Z

Cross-SDK Consistency Review ✅

This PR improves cross-SDK consistency by aligning Python's session event model with Go's approach.

Summary of findings:

SDK	Event dispatch pattern	`sendAndWait` return type
Python (this PR)	`match event.data: case AssistantMessageData()`	`SessionEvent \| None`
Go	`switch event.Data.(type)` / type assertion	`*SessionEvent`
.NET	`event is AssistantMessageEvent` (polymorphic JSON)	`AssistantMessageEvent?`
TypeScript	`event.type === "assistant.message"` (discriminated union)	`AssistantMessageEvent \| undefined`

What this PR does well:

✅ Python now generates dedicated per-event payload dataclasses (AssistantMessageData, SessionIdleData, etc.), matching Go's approach of strongly-typed event data
✅ The match event.data: case XxxData() pattern is idiomatic Python and semantically parallel to Go's type switch
✅ Forward-compatibility is preserved via RawSessionEventData for unknown event types (parallel to Go's RawSessionEventData)
✅ Docs updated consistently across language examples

Pre-existing inconsistency (not introduced by this PR):
Node.js and .NET's sendAndWait/SendAndWaitAsync return a pre-narrowed AssistantMessageEvent type directly (so callers can access .data.content without further narrowing), while Python and Go return the base SessionEvent type requiring an additional type check. This difference predates this PR and is not in scope here.

No action needed from a cross-SDK consistency perspective — this PR is a net improvement to consistency.

Generated by SDK Consistency Review Agent for issue #1063 · ● 807.8K · ◷

stephentoub requested a review from a team as a code owner April 11, 2026 18:51

Copilot AI review requested due to automatic review settings April 11, 2026 18:51

Copilot started reviewing on behalf of stephentoub April 11, 2026 18:52 View session

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stephentoub force-pushed the stephentoub/align-python-event-generation branch from 723b9d2 to 0b80129 Compare April 13, 2026 02:46

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stephentoub and others added 10 commits April 14, 2026 08:28

Clarify typed Python event examples

96de885

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Align Python generator formats

789b98e

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Fix SDK test formatting

9fee14e

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use runtime checks in Python README

9020a58

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use isinstance in Python event examples

591ac03

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use isinstance for broadcast events

adc2d9b

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Use match for Python event data

9a0a8f2

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Fix Python SDK Ruff failures

e6d65d9

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

stephentoub and others added 2 commits April 14, 2026 08:34

Remove Python session event shims

a98118d

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Preserve Python event helper types

698dc0d

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

stephentoub force-pushed the stephentoub/align-python-event-generation branch from cb1499d to 698dc0d Compare April 14, 2026 13:23

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Fix Node.js lint and generated file drift

6c3e675

Normalize trailing whitespace in pyDocstringLiteral to prevent cross-platform codegen drift, and reformat test file with Prettier. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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github-actions bot reviewed Apr 14, 2026

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stephentoub added this pull request to the merge queue Apr 14, 2026

Merged via the queue into main with commit 6722743 Apr 14, 2026
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stephentoub deleted the stephentoub/align-python-event-generation branch April 14, 2026 15:30

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stephentoub commented Apr 11, 2026

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github-actions bot commented Apr 14, 2026

Cross-SDK Consistency Review ✅

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5 participants