mypy warns about invalid types for json argument

[hmoffatt]

I have warnings about invalid types for the json argument, that didn't occur when using types-requests.

The changes in v2.34.1 changed the errors, but did not fix them.

typecheck.py:6: error: Argument "json" to "post" has incompatible type "dict[str, Collection[str]]"; expected "JsonType"  [arg-type]
typecheck.py:9: error: Argument "json" to "post" has incompatible type "dict[str, object]"; expected "JsonType"  [arg-type]

Reproduction Steps

import requests

def fn(d: dict[str, str]) -> None:
    j = {"foo": d, "bar": "hi"}
    requests.post("https://example.com", json=j)

    k = {"foo": d, "bool": True}
    requests.post("https://example.com", json=k)

It seems ok if a literal is used without the intermediate variable:

    requests.post("https://example.com", json={"foo": d, "bar": "hi"})
    requests.post("https://example.com", json={"foo": d, "bool": True})

System Information

{
  "chardet": {
    "version": null
  },
  "charset_normalizer": {
    "version": "3.4.7"
  },
  "cryptography": {
    "version": ""
  },
  "idna": {
    "version": "3.15"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.13.5"
  },
  "platform": {
    "release": "6.12.74+deb13+1-amd64",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "",
    "version": null
  },
  "requests": {
    "version": "2.34.1"
  },
  "system_ssl": {
    "version": "30500050"
  },
  "urllib3": {
    "version": "2.7.0"
  },
  "using_charset_normalizer": true,
  "using_pyopenssl": false
}

[nateprewitt]

This looks like a current limitation of mypy. pyright and ty are both able to detect the typing is correct for these cases. mypy seems to be trying to group all possible types into the single highest common type. That's why we get Collection[str] and object neither of which is particularly helpful. In the context of calling Requests, it understands the types are compatible though.

The reason types-requests worked is because there was no type here, it was Any. We may have to degrade to shutting off typing to support mypy but I'd wanted to avoid that. Let me investigate a bit more to see if we can get something working.

[hmoffatt]

I added explicit types to my intermediate variables as a solution for my case.

[nateprewitt]

I think eventually we want to expose a subset of the types in _types.py publicly which would include JsonType. That would simplify manually typing input, but that's pretty poor ergonomics for using the json parameter. Given this affects 1 of 3 type checkers (but it's the most popular one), I think I'm going to leave this open for now.

I want to hopefully get some more data points on how much friction this is actually causing. I assume it'll be high but we should quantify that before making a decision. If it does prove to be a significant pain point, we'll look at moving to Any.