Compare objects MRO with encoders at runtime

[ramnes]

The current implementation doesn't handle subclass instances when fastapi.encoders.ENCODERS_BY_TYPE is modified after fastapi.encoders import.

For example, in this example we could expect the / route to return an ObjectId string. But currently, it returns {} instead:

import bson
import uvicorn
from fastapi import FastAPI
from fastapi.encoders import ENCODERS_BY_TYPE


ENCODERS_BY_TYPE |= {bson.ObjectId: str}

app = FastAPI()


class CustomObjectId(bson.ObjectId):
    pass


@app.get("/")
def get_child():
    return CustomObjectId()


uvicorn.run(app)

This PR resolves this (and simplifies the code, as well).

Continuation of #755 and #756.

cc @RmStorm

[github-actions]

📝 Docs preview for commit 1eecf8d at: https://63879599e9e83c30ae90119c--fastapi.netlify.app

[ramnes]

@tiangolo While it wasn't my first purpose, it also seems to make jsonable_encoder ~40% faster on the benchmark you used in #756:

(.venv) $ # without #5718
(.venv) $ pip install -q -I https://github.com/tiangolo/fastapi/archive/83bcdc40d853e50752d4d4a30bbc8b23a8dbc4c1.zip
(.venv) $ hyperfine --warmup=3 'python performance.py'
Benchmark 1: python performance.py
  Time (mean ± σ):     27.843 s ±  0.308 s    [User: 27.651 s, System: 0.162 s]
  Range (min … max):   27.555 s … 28.495 s    10 runs

(.venv) $ # with #5718
(.venv) $ pip install -q -I https://github.com/Refty/fastapi/archive/1eecf8dda26e23c7f3b6dcd30f9a27171f5ae217.zip
(.venv) $ hyperfine --warmup=3 'python performance.py'
Benchmark 1: python performance.py
  Time (mean ± σ):     16.105 s ±  0.247 s    [User: 15.981 s, System: 0.110 s]
  Range (min … max):   15.907 s … 16.663 s    10 runs

If you want to replicate, I just changed the ranges to make it work better with hyperfine:

import time
import uuid
from fastapi.encoders import jsonable_encoder


class SubStr(str):
    pass


class MyUuid:
    def __init__(self, uuid_string: str):
        self.uuid = uuid_string

    def __str__(self):
        return self.uuid

    @property
    def __class__(self):
        return uuid.UUID

    @property
    def __dict__(self):
        """Spoof a missing __dict__ by raising TypeError, this is how
        asyncpg.pgroto.pgproto.UUID behaves"""
        raise TypeError("vars() argument must have __dict__ attribute")


test_input_3 = [MyUuid(str(uuid.uuid4())) for _ in range(1_000)]

for _ in range(10_000):
    jsonable_encoder(test_input_3)

[PraveenNanda124]

Good work

[github-actions]

📝 Docs preview for commit bdc4ac5 at: https://63b9e627bed8f476843378f2--fastapi.netlify.app

[ramnes]

I just updated the first message with a code example to make the problem clearer.

@tiangolo Any hint on the direction that this PR should take?

[ramnes]

Also, FWIW, Pydantic uses the same approach: https://github.com/pydantic/pydantic/blob/f55515820a407c5d31c45a7b0307925eecf21f34/pydantic/json.py#L82-L90

[dkatzan]

LGTM
I was facing a similar issue, and wondered why did fastapi took a different approach on this from pydantic
consider using the snippet u added to the PR as a base for a test for this fix

[ramnes]

Thanks for the feedback @dkatzan! Yeah, I can definitely add a test or anything else that would help; I'd prefer a confirmation that it's the correct approach before putting more work into that PR though, especially since @tiangolo wrote most of the code I'm removing. 😅

[ramnes]

rebased

[ramnes]

rebased

[ramnes]

rebased

[ramnes]

rebased