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[Flask-Cors] Update type annotation for origins to also allow Pattern #15825

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[Flask-Cors] Update type annotation for origins to also allow Pattern #15825

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[Flask-Cors] Update type annotation for origins to also allow Pattern
wvanbergen May 23, 2026
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pre-commit-ci[bot] May 23, 2026
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2 changes: 1 addition & 1 deletion stubs/Flask-Cors/flask_cors/core.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ _MultiDict: TypeAlias = Any # werkzeug is not part of typeshed
@type_check_only
class _Options(TypedDict, total=False):
resources: dict[str, dict[str, Any]] | list[str] | str | None
origins: str | list[str] | None
origins: str | Pattern[str] | Iterable[str | Pattern[str]] | None
methods: str | list[str] | None
expose_headers: str | list[str] | None
allow_headers: str | list[str] | None
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@brianschubert brianschubert Jun 7, 2026

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Unless I'm missing something, it appears that these function assume that the options have already been processed with serialize_options, which wraps a single string or pattern object in a list to ensure that origins is iterable. They'll raise a TypeError if you attempt to use a plain pattern object.

It also doesn't appear that None (or [None]) is a valid value (will also raise a TypeError). I'm guessing that that was added since the options are accessed with options.get(...), which suggests that None could be returned. But in actuality the options dict is pre-populated with the values from DEFAULT_OPTIONS, which sets non-None defaults, so I don't think a None value is ever valid?

A few examples of what I'm talking about:

# Non-iterable origins wrapped in list
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; print(c.serialize_options({"origins": "foo"}))'
{'origins': ['foo'], 'allow_headers': [None]}

# Raise on plain pattern object for origins
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; import re; print(c.get_cors_origins({"origins": re.compile("foo")}, "foo"))'
TypeError: argument of type 're.Pattern' is not a container or iterable

# Raise on None for origins
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; import re; print(c.get_cors_origins({"origins": None}, "foo"))'
TypeError: argument of type 'NoneType' is not a container or iterable

# Raise on [None] for origins
$ uv run -w flask_cors python3 -c 'import flask_cors.core as c; import re; print(c.get_cors_origins({"origins": [None]}, "foo"))'
TypeError: argument of type 'NoneType' is not a container or iterable

Does that match your experience?

The same appears to be true for allow_headers, so I'd suggest using the same type for it. It also appears that some of the other options can't be None in practice -- up to you if you want to try to fix those while we're here.

Suggested change
origins: str | Pattern[str] | Iterable[str | Pattern[str]] | None
methods: str | list[str] | None
expose_headers: str | list[str] | None
allow_headers: str | list[str] | None
origins: Iterable[str | Pattern[str]]
methods: str | list[str] | None
expose_headers: str | list[str] | None
allow_headers: Iterable[str | Pattern[str]]

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5 changes: 3 additions & 2 deletions stubs/Flask-Cors/flask_cors/extension.pyi
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
from collections.abc import Callable, Iterable
from datetime import timedelta
from logging import Logger
from re import Pattern
from typing import Any

import flask
Expand All @@ -13,7 +14,7 @@ class CORS:
app: flask.Flask | flask.Blueprint | None = None,
*,
resources: dict[str, dict[str, Any]] | list[str] | str | None = ...,
origins: str | list[str] | None = ...,
origins: str | Pattern[str] | Iterable[str | Pattern[str]] | None = ...,
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@brianschubert brianschubert Jun 7, 2026

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Per above, it doesn't appear that passing None is valid.

Suggested change
origins: str | Pattern[str] | Iterable[str | Pattern[str]] | None = ...,
origins: str | Pattern[str] | Iterable[str | Pattern[str]] = ...,

methods: str | list[str] | None = ...,
expose_headers: str | list[str] | None = ...,
allow_headers: str | list[str] | None = ...,
Expand All @@ -28,7 +29,7 @@ class CORS:
app: flask.Flask,
*,
resources: dict[str, dict[str, Any]] | list[str] | str = ...,
origins: str | list[str] = ...,
origins: str | Pattern[str] | Iterable[str | Pattern[str]] = ...,
methods: str | list[str] = ...,
expose_headers: str | list[str] = ...,
allow_headers: str | list[str] = ...,
Expand Down
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