无法使用 Uvicorn 修复“'cannot convert dictionary update sequence element #0 to a sequence'”

Question

我有以下代码，使用 FastApi 和 Uvicorn 实现 ASGI 服务器。它应该通过 post 请求获取上传的图像，并在返回响应之前用模型对其进行分类。该错误似乎与 Uvicorn 有关，但我不知所措。任何帮助将非常感激。有没有人见过这样的错误？这是代码：

import uvicorn
from fastapi import FastAPI, File, UploadFile
import sys

from PIL import Image
from io import BytesIO
import numpy as np

import tensorflow as tf
from tensorflow import keras
from tensorflow.keras import layers
import matplotlib.pyplot as plt
from tensorflow.keras.preprocessing import image
import PIL
import sys 
from cv2 import cv2
from scipy import misc
import os

import shutil
from pathlib import Path
from tempfile import NamedTemporaryFile
from typing import Callable

app = FastAPI()

model = keras.models.load_model('best_model6.h5')
input_shape = (180, 180) 

@app.post('/api/predict')
async def predict_image(file: UploadFile = File(...)):

    suffix = Path(file.filename).suffix

    with NamedTemporaryFile(delete=False, suffix=suffix) as tmp:
        shutil.copyfileobj(file.file, tmp)
        tmp_path = Path(tmp.name)
    
    img = keras.preprocessing.image.load_img(
    tmp_path, target_size=input_shape
)
    
    img_array = image.img_to_array(img)

    img_array = tf.expand_dims(img_array, 0)  # Create batch axis

    predictions = model.predict(img_array)
    score = predictions[0]

    file.file.close()
    tmp_path.unlink()
    
    return score


if __name__ == "__main__":
    uvicorn.run(app, port=8080, host='0.0.0.0', debug=True)

错误是：

ValueError: [TypeError('cannot convert dictionary update sequence element #0 to a sequence'), TypeError('vars() argument must have __dict__ attribute')]

以及整个追溯：

Traceback (most recent call last):
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/uvicorn/protocols/http/h11_impl.py", line 373, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/uvicorn/middleware/proxy_headers.py", line 75, in __call__
    return await self.app(scope, receive, send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/uvicorn/middleware/debug.py", line 96, in __call__
    raise exc from None
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/uvicorn/middleware/debug.py", line 93, in __call__
    await self.app(scope, receive, inner_send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/fastapi/applications.py", line 208, in __call__
    await super().__call__(scope, receive, send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/applications.py", line 112, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/middleware/errors.py", line 181, in __call__
    raise exc
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/middleware/errors.py", line 159, in __call__
    await self.app(scope, receive, _send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/exceptions.py", line 82, in __call__
    raise exc
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/exceptions.py", line 71, in __call__
    await self.app(scope, receive, sender)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/routing.py", line 656, in __call__
    await route.handle(scope, receive, send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/routing.py", line 259, in handle
    await self.app(scope, receive, send)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/starlette/routing.py", line 61, in app
    response = await func(request)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/fastapi/routing.py", line 234, in app
    response_data = await serialize_response(
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/fastapi/routing.py", line 148, in serialize_response
    return jsonable_encoder(response_content)
  File "/Users/.../Desktop/project/venv/lib/python3.9/site-packages/fastapi/encoders.py", line 144, in jsonable_encoder
    raise ValueError(errors)
ValueError: [TypeError('cannot convert dictionary update sequence element #0 to a sequence'), TypeError('vars() argument must have __dict__ attribute')]

Answer 1

来自 Keras 模型的 predit 函数的 return 是一个 Numpy 预测数组 (see here)，每个预测也是一个 numpy 数组。

但是 FastApi 在响应中使用 jsonable_encoder (see here) 并且 numpy 数组是不可接受的。您应该转换为 list(score.tolist())，例如，转换为 return 预测分数。在同一个 link 中，您会看到可以 return 直接响应而不使用 jsonable_encoder

希望对您有所帮助。祝你好运

无法使用 Uvicorn 修复“'cannot convert dictionary update sequence element #0 to a sequence'”

Trouble fixing "'cannot convert dictionary update sequence element #0 to a sequence'" with Uvicorn

python

server

tensorflow

fastapi

uvicorn