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Add ContentType generic to Response #2547

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Add ContentType generic to Response #2547

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991327b
Add `ContentType` generic to `Response`
Kludex Mar 19, 2024
47dbc98
Bump mypy
Kludex Mar 19, 2024
ba8a89b
Fix mypy
Kludex Mar 19, 2024
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2 changes: 1 addition & 1 deletion pyproject.toml
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Expand Up @@ -27,7 +27,7 @@ classifiers = [
]
dependencies = [
"anyio>=3.4.0,<5",
"typing_extensions>=3.10.0; python_version < '3.10'",
"typing_extensions>=4.4.0; python_version < '3.13'",
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default= was introduced in this version: https://typing-extensions.readthedocs.io/en/latest/#typing_extensions.TypeVar

]

[project.optional-dependencies]
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2 changes: 1 addition & 1 deletion requirements.txt
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Expand Up @@ -4,7 +4,7 @@
# Testing
coverage==7.4.3
importlib-metadata==7.0.1
mypy==1.8.0
mypy==1.9.0
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Last release supports default=.

ruff==0.1.15
typing_extensions==4.10.0
types-contextvars==2.4.7.3
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26 changes: 17 additions & 9 deletions starlette/responses.py
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Expand Up @@ -4,6 +4,7 @@
import json
import os
import stat
import sys
import typing
import warnings
from datetime import datetime
Expand All @@ -21,14 +22,21 @@
from starlette.datastructures import URL, MutableHeaders
from starlette.types import Receive, Scope, Send

if sys.version_info >= (3, 13): # pragma: no cover
from typing import TypeVar
else:
from typing_extensions import TypeVar

class Response:
Content = TypeVar("Content", default=typing.Any)


class Response(typing.Generic[Content]):
Comment on lines +30 to +33
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It seems to me like the reality is that the default should be str | bytes given what Response accepts. Then subclasses like StreamingResponse should override this generic with whatever they accept. If we make the default typing.Any then Response is not correctly typed. Since we're setting the default in this PR we might as well choose an appropriate value.

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I'm not changing this in this PR. There was a previous attempt to change the type to str | bytes | None, and it was reverted - I don't remember the reason.

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Ok. It would be good to find that reason.

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#2242

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Ok I see. So yes the right thing to do would be to make a BaseResponse and make Response just one of the many concrete classes:

_ResponseDataT = TypeVar('_ResponseDataT')

class BaseResponse(Generic[_ResponseDataT]):
    def render(self, data: _ResponseDataT | None) -> bytes:
        raise NotImplementedError

class Response(BaseResponse[str | bytes]):
    ...

_JsonData = str | bytes | float | int | None | ...

class JsonResponse(BaseResponse[_JsonData]):
    ...

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But the Response class does have the .render() method... So I don't see how I'd that? I can't make the classes stop inheriting Response, because that would be a breaking change.

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Yes, this is also what I think is unreasonable about Starlette. For example, StreamResponse and FileReponse do not use render, but they inherit this method.

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Are you suggesting adding a breaking change then?

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Yes. 😊

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Can we do some naming to make it a non-breaking change or minimize the breakage? We could leave the render() method on the base class but mark it as deprecated vi a warning. Adding a BaseResponse class is not a breaking change. I think removing the render() method from eg StreamingResponse (because it inherits from BaseResponse and not Response) would also be okay.

media_type = None
charset = "utf-8"

def __init__(
self,
content: typing.Any = None,
content: Content | None = None,
status_code: int = 200,
headers: typing.Mapping[str, str] | None = None,
media_type: str | None = None,
Expand All @@ -41,7 +49,7 @@ def __init__(
self.body = self.render(content)
self.init_headers(headers)

def render(self, content: typing.Any) -> bytes:
def render(self, content: Content | None) -> bytes:
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| was introduced in 3.10.

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We use __future__.annotations, and the pipeline passes. 👀

if content is None:
return b""
if isinstance(content, bytes):
Expand Down Expand Up @@ -170,20 +178,20 @@ class PlainTextResponse(Response):
media_type = "text/plain"


class JSONResponse(Response):
class JSONResponse(Response[Content]):
media_type = "application/json"

def __init__(
self,
content: typing.Any,
content: Content,
status_code: int = 200,
headers: typing.Mapping[str, str] | None = None,
media_type: str | None = None,
background: BackgroundTask | None = None,
) -> None:
super().__init__(content, status_code, headers, media_type, background)

def render(self, content: typing.Any) -> bytes:
def render(self, content: Content | None) -> bytes:
return json.dumps(
content,
ensure_ascii=False,
Expand All @@ -207,9 +215,9 @@ def __init__(
self.headers["location"] = quote(str(url), safe=":/%#?=@[]!$&'()*+,;")


Content = typing.Union[str, bytes]
SyncContentStream = typing.Iterable[Content]
AsyncContentStream = typing.AsyncIterable[Content]
_Content = typing.Union[str, bytes]
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Just to confirm, this is a breaking change right?

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Oh yeah, it is...

SyncContentStream = typing.Iterable[_Content]
AsyncContentStream = typing.AsyncIterable[_Content]
ContentStream = typing.Union[AsyncContentStream, SyncContentStream]


Expand Down