✨ Add support for PEP695 TypeAliasType #11140

dev-loki · 2024-02-13T20:43:11Z

Fixes: #10719
Discussed (by others) in: #10662

Adds support for PEP695.

Sidesupport (please check if intended!): Only loads *_py312 files for python3.12 and later, as only the test introduces syntax not compatible for python < 3.12.

def some_complex_function():
    return 42
    
type DependedVariable = Annotated[int, some_complex_function]

Using DependedVariable in route dependencies will now work :).

dev-loki · 2024-02-13T20:54:11Z

Kind of unhappy with the amount of hoopsI jump through to not let coverage/pytest really see the test code, as it is a true SyntaxError in all python Version before 3.12.

Maybe there is a better idea?

dev-loki · 2024-02-13T21:10:00Z

tests/conftest.py

+if sys.version_info < (3, 12):
+    collect_ignore_glob = ["*_py312.py"]


Shall we add that to the previous versions too?

tests/utils.py

UltimateLobster · 2025-01-05T06:01:42Z

It's a shame to see this PR being ignored for so long, seems like a useful feature to support.
Is there a way I can help this get merged? If I were to review this PR myself would it help? (or will it not matter since I'm not actually a maintiner?)

Viicos · 2025-02-04T11:09:18Z

fastapi/dependencies/utils.py

@@ -325,6 +331,9 @@ def analyze_param(
    depends = None
    type_annotation: Any = Any
    use_annotation: Any = Any
+    if TypeAliasType is not None and isinstance(annotation, TypeAliasType):


This is not going to work as expected for all cases; see litestar-org/litestar#3982 (comment).

Is there a unit test we can design that would exhibit the non-working behaviour for the edge cases you mention?

At Pydantic, we are currently working on a third-party library to handle all these runtime inspection utilities, as per beartype/beartype#479 (comment). The package is ready for it's first release, we just need to setup the documentation infrastructure so it should be available this week.

In the meanwhile, the Pydantic implementation can be used (we have unit tests for the mentioned edge cases).

@svlandeg: we just created the typing-inspection package (docs), currently including the utility functions to inspect typing annotations (type hints evaluation isn't included for now due to the challenges mentioned).

I created a discussion on the Discourse forum to have a single place where things can be discussed. Alternatively, discussion can happen on the Github repository.

cc @tiangolo

Viicos · 2025-02-04T11:09:39Z

fastapi/dependencies/utils.py

@@ -64,6 +64,12 @@
 from starlette.websockets import WebSocket
 from typing_extensions import Annotated, get_args, get_origin

+try:
+    from typing_extensions import TypeAliasType


typing_extensions.TypeAliasType was added in 4.6.0, but 4.8.0 is required:

fastapi/pyproject.toml

Lines 45 to 48 in ae724b0

dependencies = [

"starlette>=0.40.0,<0.46.0",

"pydantic>=1.7.4,!=1.8,!=1.8.1,!=2.0.0,!=2.0.1,!=2.1.0,<3.0.0",

"typing-extensions>=4.8.0",

github-actions · 2025-02-18T14:45:34Z

📝 Docs preview for commit 8dc8298 at: https://d462d901.fastapitiangolo.pages.dev

svlandeg · 2025-02-18T14:46:37Z

Hi @dev-loki, thanks for this contribution, and apologies for the delay in reviewing! There is quite a backlog of PR's to work on, and we're currently trying to manage & prioritize the queue more efficiently. Thanks for your patience!

@UltimateLobster: yes - a review by other users (even when they are not maintainers) is always useful. Feel free to be as verbose & nitpicking as you want. For instance, you can be very explicit about which parts you're happy with, which parts you're unsure, what you think is important to change or perhaps some fixes where you note that they are a matter of preference and not necessary. It's always easier for us if you're more verbose, so we understand exactly how you reviewed and what you think of the proposed changes. In general, helping with checking that the PR is up-to-date, passes the CI, is consistent with the rest of the code base, and contains the correct unit checks, is really helpful too.

@Viicos: thanks for the review!

github-actions · 2025-07-09T16:47:15Z

📝 Docs preview for commit 4b06230 at: https://376f8223.fastapitiangolo.pages.dev

YuriiMotov · 2025-07-09T16:59:07Z

@dev-loki, thank you for your efforts!

Could you please take a look at failed tests and address this comment?

YuriiMotov · 2025-07-22T17:36:06Z

In case @dev-loki is busy or not interested in this PR anymore, does anybody else wants to take this over?

cstruct · 2025-07-23T14:37:32Z

@YuriiMotov if someone else has to take this over I could do it. I would love to see this land!

dev-loki · 2025-07-23T15:25:58Z

@YuriiMotov if someone else has to take this over I could do it. I would love to see this land!

Yes feel free to do it :). I don't have time anymore and also lost context after that time (since then I switched jobs, living places and got another daughter going to school :D)

YuriiMotov · 2025-07-23T17:06:05Z

Let's close this PR then.
@dev-loki, thanks for your efforts!

@cstruct, feel free to take this over and open new PR!

cstruct · 2025-07-23T18:01:15Z

@dev-loki thank you for your work! I'll try to base my continued work on your commits to keep the history. Hope your life changes have been good!

dev-loki · 2025-07-23T18:09:18Z

Oh yes they have. In every single aspect :). Thank you for that and for your time form open source ♥️ -------- Ursprüngliche Nachricht --------Am 23.07.25 20:01 schrieb Albin Skott :cstruct left a comment (fastapi/fastapi#11140) @dev-loki thank you for your work! I'll try to base my continued work on your commits to keep the history. Hope your life changes have been good! —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***> [ { ***@***.***": "http://schema.org", ***@***.***": "EmailMessage", "potentialAction": { ***@***.***": "ViewAction", "target": "#11140 (comment)", "url": "#11140 (comment)", "name": "View Pull Request" }, "description": "View this Pull Request on GitHub", "publisher": { ***@***.***": "Organization", "name": "GitHub", "url": "https://github.com" } } ]

dev-loki added 5 commits February 13, 2024 20:33

Add support for PEP695 TypeAliasType

85044cf

Add tests for pepe695 compatibility

1d6f28a

Make pytest ignore py312 files for older py

9d215ad

'fix' mypy issue

4ca7f7e

ignore py312 file for coverage: SyntaxError

fb15e0d

Exclude faulty branch from coverage

2fa1a2e

dev-loki commented Feb 13, 2024

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tiangolo added feature New feature or request p3 labels Mar 13, 2024

Viicos reviewed Feb 4, 2025

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svlandeg changed the title ~~Add support for PEP695 TypeAliasType~~ ✨ Add support for PEP695 TypeAliasType Feb 18, 2025

Merge branch 'master' into bugfix/allow-pep695-type-alias

8dc8298

Viicos mentioned this pull request Feb 24, 2025

✨ Add type alias syntax support for dependency injection #13401

Closed

Merge branch 'master' into bugfix/allow-pep695-type-alias

4b06230

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YuriiMotov closed this Jul 23, 2025

cstruct mentioned this pull request Jul 24, 2025

✨ Add support for PEP695 TypeAliasType #13920

Open

		if sys.version_info < (3, 12):
		collect_ignore_glob = ["*_py312.py"]

	dependencies = [
	"starlette>=0.40.0,<0.46.0",
	"pydantic>=1.7.4,!=1.8,!=1.8.1,!=2.0.0,!=2.0.1,!=2.1.0,<3.0.0",
	"typing-extensions>=4.8.0",

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✨ Add support for PEP695 TypeAliasType #11140

✨ Add support for PEP695 TypeAliasType #11140

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