Make http.cookies.SimpleCookie non-generic

[flaeppe]

Fixes: #10700

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

steam.py (https://github.com/Gobot1234/steam.py)
+ steam/http.py:180: error: The type "type[SimpleCookie]" is not generic and not indexable [misc]+ steam/http.py:181: error: The type "type[SimpleCookie]" is not generic and not indexable [misc]
aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/helpers.py:942:24: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/helpers.py:942:24: note: Error code "type-arg" not covered by "type: ignore" comment+ aiohttp/helpers.py:942:24: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-type-arg for more info+ aiohttp/helpers.py:945:26: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/helpers.py:1028:43: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/cookiejar.py:66:53: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/cookiejar.py:169:22: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/cookiejar.py:235:35: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/cookiejar.py:246:25: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/connector.py:228:23: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/client_reqrep.py:377:12: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/client_reqrep.py:710:23: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]+ aiohttp/web_request.py:574:17: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]
starlette (https://github.com/encode/starlette)
+ tests/test_responses.py:347: error: "SimpleCookie" expects no type arguments, but 1 given [type-arg]

[srittau]

Thanks! While the primer hits indicate that this change is disruptive, looking at the hits in depth indicates that the code in question can be simplified significantly. Currently, using SimpleCookie requires an explicit type annotation to specify the generic type (which can only be str), so I think the benefits outweighs the disruption significantly.

I'll leave it open for now if other maintainers want to chime in.

[AlexWaygood]

I'm not too familiar with this module, so this may be a dumb question, but should even BaseCookie be generic? I can't find any uses on grep.app where BaseCookie is subscripted with anything other than str, and the docs don't shine any light on a situation where you might have a Morsel[bytes] or whatever as the value in a BaseCookie dictionary.

>>> from http.cookies import BaseCookie
>>> b = BaseCookie()
>>> b['foo'] =b'bar'
>>> b['foo'
<Morsel: foo=b'bar'>
>>> _.coded_value
"b'bar'"
>>> type(b['foo'].coded_value)
<class 'str'>

[flaeppe]

Yeah, I don't know either. I'm getting a feeling it might be about conversion between formats rather than conversion to e.g. bytes. But I'm only guessing here

[JelleZijlstra]

Chances are it's a Python 2 remnant: maybe in Python 2 you could have both str and unicode cookies.

[AlexWaygood]

Looks like both classes were originally made generic in:

• Improve http #248

But there's no explanation in that PR thread as to why

[flaeppe]

Documentation for BaseCookie.value_encode says that coded_value will always "be converted to a string". Where it is set as Morsel.coded_value. So I suppose it should be valid to declare BaseCookie[int] and then implement a value_decode that parses an int from a str?

I'm not too familiar with this module, so this may be a dumb question, but should even BaseCookie be generic? I can't find any uses on grep.app where BaseCookie is subscripted with anything other than str, and the docs don't shine any light on a situation where you might have a Morsel[bytes] or whatever as the value in a BaseCookie dictionary.

>>> from http.cookies import BaseCookie
>>> b = BaseCookie()
>>> b['foo'] = b'bar'
>>> b['foo'
<Morsel: foo=b'bar'>
>>> _.coded_value
"b'bar'"
>>> type(b['foo'].coded_value)
<class 'str'>

I think an additional thing to check up on here is this

>>> from http.cookies import BaseCookie
>>> class C(BaseCookie):
... def value_encode(self, value):
... return value, value
...
>>> c = C()
>>> c["foo"] = b"bar"
>>> c["foo"]
<Morsel: foo=b'bar'>
>>> c["foo"].coded_value
b'bar'
>>> type(c["foo"].coded_value)
<class 'bytes'>
>>> c["foo"].output()
"Set-Cookie: foo=b'bar'"

Morsel.coded_value is always stringified before it's sent. At least that's what I interpret from "coded_value will always be converted to a string".

Funny thing is though, just because you've declared BaseCookie[int] it won't make .coded_value return int. And the only control over that is to enforce usage of Morsel[int] as set value.

Consider this program, which passes, but coded_value is <class 'str'>

fromhttp.cookiesimportBaseCookie, MorselclassC(BaseCookie[int]):
...
c=C()
c["foo"] ="1"coded_value=c["foo"].coded_valuereveal_type(coded_value) # Revealed type is "builtins.int"

But if you'd instead use below, types align.

m=Morsel[int]()
m.set("foo", "1", 1)
c["foo"] =m

[AlexWaygood]

OK cool, sounds like BaseCookie should remain generic, then, in order to allow flexibility for hypothetical user subclasses of BaseCookie. Thanks for the research and the thorough explanation @flaeppe!!

[AlexWaygood]

LGTM