[BugFix]: Fix local mypy issues by hickeyma · Pull Request #34739 · vllm-project/vllm

hickeyma · 2026-02-17T19:43:44Z

Purpose

When you run pre-commit in local dev environment, you get the following mypy errors:

$ pre-commit run --all-files    

ruff check..........................................................................................Passed
ruff format.........................................................................................Passed
typos...............................................................................................Passed
clang-format........................................................................................Passed
Lint GitHub Actions workflow files..................................................................Passed
pip-compile.........................................................................................Passed
reformat nightly_torch_test.txt to be in sync with test.in..........................................Passed

Run mypy locally for lowest supported Python version................................................Failed
- hook id: mypy-local
- exit code: 1

$ mypy --python-version 3.10 --follow-imports skip 
vllm/entrypoints/openai/chat_completion/protocol.py:466: error: Value of type variable "_DataclassT" of "replace" cannot be "StructuredOutputsParams"  [type-var]
vllm/entrypoints/openai/responses/protocol.py:339: error: Unexpected keyword argument "json" for "StructuredOutputsParams"  [call-arg]
vllm/entrypoints/openai/completion/protocol.py:272: error: Value of type variable "_DataclassT" of "replace" cannot be "StructuredOutputsParams"  [type-var]
vllm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py:938: error: Module has no attribute "sched_setaffinity"  [attr-defined]
vllm/entrypoints/openai/responses/serving.py:503: error: Value of type variable "_DataclassT" of "replace" cannot be "StructuredOutputsParams"  [type-var]
Found 5 errors in 5 files (checked 645 source files)

[...]

This PR fixes the issues as shown below.

MyPy issues handled as follows:

Pydantic dataclasses does not satisfy mypy's type system with replace(), even though they are fully compatible at runtime. Therefore, ignore
Skipped import issue that StructuredOutputsParams has with json prioperty in vllm/entrypoints/openai/responses/protocol.py. Therefore, ignore as enabling the imports raises lot of other issues which are unrelated.
sched_setaffinity() is a Linux only OS command and therefore added a check in llm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py for it.

Additionally:

Renamed json import because property called json in class also in vllm/sampling_params.py. This is for hygiene reasons.

Essential Elements of an Effective PR Description Checklist

The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
The test plan, such as providing test command.
The test results, such as pasting the results comparison before and after, or e2e results
(Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
(Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

gemini-code-assist

Code Review

This pull request addresses several mypy issues found during local development. The changes primarily involve adding type: ignore comments to suppress type errors related to Pydantic dataclasses and dataclasses.replace, which is a reasonable approach for these known mypy limitations. A platform-specific check for os.sched_setaffinity has been correctly added to prevent errors on non-Linux systems. However, there's a potential issue in vllm/sampling_params.py where import json_mod is used. This seems to assume a new file that isn't part of the PR. I've suggested using a standard alias import json as json_mod to resolve the name clash cleanly.

vllm/sampling_params.py

njhill · 2026-02-18T01:07:02Z

Thanks @hickeyma, I haven't looked closely but I think this may be a dup of #34693?

hickeyma · 2026-02-18T09:20:38Z

Thanks @hickeyma, I haven't looked closely but I think this may be a dup of #34693?

Thanks @njhill for making me aware of it, I didn't see it when I checked before I started my PR. Yes, there is duplicate for StructuredOutputsParams replace() issue but not for the other fixes. Also, I took a different approach to StructuredOutputsParams replace() issue as commented in #34693 (review).

hmellor

As mentioned in the other PR, you could try

vllm/vllm/config/utils.py

Lines 105 to 113 in 1391378

    
           def replace(dataclass_instance: ConfigT, /, **kwargs) -> ConfigT: 
        
               """Like [`dataclasses.replace`](https://docs.python.org/3/library/dataclasses.html#dataclasses.replace), 
        
               but compatible with Pydantic dataclasses which use `pydantic.fields.Field` instead 
        
               of `dataclasses.field`""" 
        
               cls = type(dataclass_instance) 
        
               dataclass_dict = dataclass_instance.__dict__ 
        
               dataclass_dict = {k: v for k, v in dataclass_dict.items() if is_init_field(cls, k)} 
        
               dataclass_dict.update(kwargs) 
        
               return cls(**dataclass_dict)

which is pydntic compatible

hickeyma · 2026-02-19T11:22:24Z

Thanks @hmellor for pointing out an existing implementation of replace(). What is the value of adding the override method? If its just for mypy type error, if so is it worth the overhead and potential maintenance?

hickeyma · 2026-02-19T11:29:28Z

Ok, I think I see. You lose the validation otherwise.

hickeyma · 2026-02-19T11:58:47Z

@hmellor I have updated to use the pydantic compatible replace() function.

hmellor · 2026-02-19T16:18:16Z

The main reason that dataclasses.replace isn't compatible with pydantic dataclasses is that it doesn't look inside pydantic.fields.Field to check for init. So then it will try to initialise the dataclass with fields that are post-init-only. This reimplementation respects the init by checking is_init_field.

And yes it allows us to continue using pydantic and all the validation that comes with it

vllm/entrypoints/openai/chat_completion/protocol.py

Review comment: - vllm-project#34739 (comment) Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

vllm/sampling_params.py

vllm/entrypoints/openai/responses/protocol.py

vllm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py

mergify · 2026-02-20T14:26:10Z

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @hickeyma.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

MyPy issues handled as follows: - Pydantic dataclasses do not satisfy mypy's type system with replace(), even though they are fully compatible at runtime. Therefore, ignore - Skipped import issue StructuredOutputsParams in vllm/entrypoints/openai/responses/protocol.py. Therefore, ignore. - sched_setaffinity is Linux only OS command and therefore added check in llm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py for it. Additionally: - Renamed json import because property called json in class also. This is for hygiene reasons. Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

Replace function from vllm/vllm/config/utils.py Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

Review comment: - vllm-project#34739 (comment) Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

hmellor

LGTM, thanks for helping reduce the mypy based weirdness in vLLM!

hickeyma · 2026-02-20T16:49:45Z

LGTM, thanks for helping reduce the mypy based weirdness in vLLM!

Thanks @hmellor for the reviews and feedback.

Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com> Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com> Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com> Signed-off-by: Andrii Skliar <askliar@nvidia.com>

Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com> Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

hickeyma requested review from ApostaC, DarkLight1337, NickLucche, aarnphm, chaunceyjiang, njhill, orozery and russellb as code owners February 17, 2026 19:43

mergify bot added frontend bug Something isn't working kv-connector labels Feb 17, 2026

gemini-code-assist bot reviewed Feb 17, 2026

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hickeyma force-pushed the fix-pre-commit branch from 4213f46 to e9fe13b Compare February 17, 2026 20:16

hickeyma mentioned this pull request Feb 18, 2026

[Bugfix] Fix mypy errors for StructuredOutputsParams by using stdlib dataclass #34693

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hmellor reviewed Feb 19, 2026

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hickeyma force-pushed the fix-pre-commit branch from e9fe13b to f1a34f0 Compare February 19, 2026 11:14

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hickeyma added a commit to hickeyma/vllm that referenced this pull request Feb 19, 2026

Remove import alias and use replace as is

693225f

Review comment: - vllm-project#34739 (comment) Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

hickeyma requested a review from hmellor February 19, 2026 16:58

hmellor reviewed Feb 20, 2026

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hickeyma requested a review from hmellor February 20, 2026 11:12

mergify bot added the needs-rebase label Feb 20, 2026

hickeyma added 3 commits February 20, 2026 15:43

Use the pydantic compatible replace to fix mypy type error

4aebfdc

Replace function from vllm/vllm/config/utils.py Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

Remove import alias and use replace as is

eebe7e1

Review comment: - vllm-project#34739 (comment) Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

hickeyma force-pushed the fix-pre-commit branch from 693225f to eebe7e1 Compare February 20, 2026 15:49

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Merge branch 'main' into fix-pre-commit

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hmellor enabled auto-merge (squash) February 20, 2026 16:45

github-actions bot added the ready ONLY add when PR is ready to merge/full CI is needed label Feb 20, 2026

vllm-bot merged commit e97c46a into vllm-project:main Feb 23, 2026
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hickeyma deleted the fix-pre-commit branch February 23, 2026 08:42

tdoublep mentioned this pull request Mar 12, 2026

[CI] Fix mypy pre-commit errors on main #36882

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	def replace(dataclass_instance: ConfigT, /, **kwargs) -> ConfigT:
	"""Like [`dataclasses.replace`](https://docs.python.org/3/library/dataclasses.html#dataclasses.replace),
	but compatible with Pydantic dataclasses which use `pydantic.fields.Field` instead
	of `dataclasses.field`"""
	cls = type(dataclass_instance)
	dataclass_dict = dataclass_instance.__dict__
	dataclass_dict = {k: v for k, v in dataclass_dict.items() if is_init_field(cls, k)}
	dataclass_dict.update(kwargs)
	return cls(**dataclass_dict)

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