python - 为什么在 except block 中发生异常时，finally block 不返回最新的异常？

Question

我写了一段代码，我使用回溯来返回异常堆栈跟踪。但是我忘了导入回溯。
文件名 - trial_main.py

from fastapi import FastAPI
from pydantic import BaseModel
import uvicorn


app = FastAPI()

class RequestJson(BaseModel):
    data: str


@app.post("/trial", status_code=200)
async def trial(req:RequestJson):
    try:
        status = "default"
        resp = {
            "status": status,
            "reason": "default reason"
        }
        
        # error point
        a = 10/0
        
        status = "complete"
        reason = "Finished converting from base64 to image"
        
        resp = {
            "status": status,
            "reason": reason
        }
    except Exception as e:
        status = "incomplete"
        resp =  {
            "status": status,
            "reason": traceback.format_exc(),
        }
    finally:
        return resp


if __name__ == '__main__':
    uvicorn.run("trial_main:app", host="0.0.0.0", port=5001, log_level="info")

令我困惑的是，由于找不到回溯模块，为什么代码没有以异常退出。而是返回之前设置的默认响应。
这是我得到的 API 响应 -

{
    "status": "default",
    "reason": "default reason"
}

这是我运行 uvicorn 服务器的终端上的输出 -

INFO:     Started server process [14744]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:5001 (Press CTRL+C to quit)
INFO:     127.0.0.1:61809 - "POST /trial HTTP/1.1" 200 OK

Api 端点 -

[POST] http://127.0.0.1:5001/trial

输入重新创建情况 -

{"data": "randomString"}

Answer 1

这里没有发生任何神秘事件。
在 try block 中，您成功地为 resp 赋值变量，然后引发异常并执行到除 block 。您正在尝试将新值分配给 resp ，但 ImportError 发生在语句的右侧，所以 resp仍然包含旧值，它将在 finally block 中返回。异常不会进一步传播，因为有 return在 finally block 中，它只是抑制异常。
为了不被 fastapi 样板分心，所有这些都可以用更简单的例子来说明

def always_return():
    """return 1"""
    try:
        res = 1
        raise Exception()
    except Exception:
        res = 1 / 0
    finally:
        return res


def never_return():
    """raises ZeroDivisionError"""

    try:
        res = 1
        raise Exception()
    except Exception:
        res = 1 / 0
    finally:
        print("finally block exists, but no return here")
    return res

>>> print(always_return())
1
>>> print(never_return())
finally block exists, but no return here
ZeroDivisionError: division by zero... traceback