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Python: handle Literal annotations in is_instance_of - #8351

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Manohar Paturi (ManoharPaturi) wants to merge 4 commits into
microsoft:mainfrom
ManoharPaturi:fix/is-instance-of-literal
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Python: handle Literal annotations in is_instance_of#8351
Manohar Paturi (ManoharPaturi) wants to merge 4 commits into
microsoft:mainfrom
ManoharPaturi:fix/is-instance-of-literal

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@ManoharPaturi

@ManoharPaturi Manohar Paturi (ManoharPaturi) commented Sep 13, 2026 •
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Motivation & Context

Workflows with a Literal message annotation on a handler crash at the first message delivery: Executor.can_handle() / _find_handler() call is_instance_of() directly on the annotation, which has no Literal case and raises TypeError: typing.Literal cannot be used with isinstance(). Registration and the builder type validation both accept Literal, and the sibling helper _matches_annotation() already implements the intended semantics, so the two validators disagree. Reported in #8350.

Description & Review Guide

  • What are the major changes? Adds a Literal case to is_instance_of() that matches by allowed values with strict member types, aligned with _matches_annotation(), so registration, validation, and delivery agree on Literal annotations.
  • What is the impact of these changes? Literal-annotated handlers work end to end; no change for any other annotation type.
  • What do you want reviewers to focus on? The member-type strictness in the new case (booleans vs integers in Literal[0, 1]-style annotations) and the three new tests.

Related Issue

Fixes #8350

Contribution Checklist

  • The code builds clean without any errors or warnings
  • All unit tests pass, and I have added new tests where possible
  • The PR follows the Contribution Guidelines
  • This PR is linked to an issue and there is no other open PR for this issue
  • This is not a breaking change.

@ManoharPaturi
Python: fix(workflows): support Literal message annotations in is_ins…
8d310f5 
…tance_of

Executor handlers annotated with a Literal message type (e.g.
`message: Literal["yes", "no"]`) pass @handler registration, executor
construction, and WorkflowBuilder type validation, but crashed at
message-delivery time with:

    TypeError: typing.Literal cannot be used with isinstance()

is_instance_of() had no case for Literal origins and fell through to
isinstance(data, Literal), which always raises. Executor.can_handle()
and Executor._find_handler() call is_instance_of() directly, so any
workflow containing such an executor failed on the first delivery.

Add a Literal case that matches by allowed values with strict member
types (bool never matches an int member), mirroring the existing
_matches_annotation() semantics used by try_coerce_to_type.
Copilot AI balanced review requested due to automatic review settings September 13, 2026 16:48
Copilot AI reviewed Sep 13, 2026

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Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

@agent-framework-automation agent-framework-automation Bot added the python Usage: [Issues, PRs], Target: Python label Sep 13, 2026
moonbox3
Evan Mattson (moonbox3) reviewed Sep 14, 2026
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Comment thread python/packages/core/agent_framework/_workflows/_typing_utils.py Outdated
Comment thread python/packages/core/agent_framework/_workflows/_typing_utils.py Outdated
Manohar paturi Manohar paturi
fix(workflows): reorder type guard before equality and delegate _matc…
d411464 
…hes_annotation to is_instance_of

- Reorder Literal evaluation to check type(data) is type(member) before data == member to prevent __eq__ side effects on mismatched types
- Remove duplicate Literal check in _matches_annotation to delegate directly to is_instance_of
- Add test verifying mismatched type with throwing __eq__ returns False without raising
eavanvalkenburg
Eduard van Valkenburg (eavanvalkenburg) approved these changes Sep 14, 2026
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@eavanvalkenburg Eduard van Valkenburg (eavanvalkenburg) left a comment

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Looks good—thanks!

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@moonbox3 Evan Mattson (moonbox3) moonbox3 left review comments
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@eavanvalkenburg Eduard van Valkenburg (eavanvalkenburg) eavanvalkenburg approved these changes
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Python: Literal handler annotations crash workflows at delivery (is_instance_of has no Literal case)

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@ManoharPaturi @eavanvalkenburg @moonbox3