FastAPI调用/people/{person_id}接口出现500内部服务器错误求助

我是Python和FastAPI新手，学习时写了一段示例代码。根路径和/people/接口运行正常，但调用/people/{person_id}接口时出现500内部服务器错误，附上代码和错误回溯，请求排查。

代码片段 #

from fastapi import FastAPI

app = FastAPI()

people = {
    "1": {
        "name": "abc", 
        "age": 27
    }, 
    "2": {
        "name": "xyz", 
        "age": 60
    }
}

@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/people/")
def get_people(
    min_age: int=0, max_age: int=100
):
    results = [person for person in people.values() if person["age"] >= min_age and person["age"] <= max_age]
    return results


@app.get("/people/{person_id}")
def get_person(person_id: int): 
    return people[person_id]

错误回溯 #

Traceback (most recent call last):
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/uvicorn/protocols/http/h11_impl.py", line 407, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/uvicorn/middleware/proxy_headers.py", line 78, in __call__
    return await self.app(scope, receive, send)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/fastapi/applications.py", line 270, in __call__
    await super().__call__(scope, receive, send)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/applications.py", line 124, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/middleware/exceptions.py", line 79, in __call__
    raise exc
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/middleware/exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/fastapi/middleware/asyncexitstack.py", line 21, in __call__
    raise e
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/fastapi/middleware/asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/routing.py", line 706, in __call__
    await route.handle(scope, receive, send)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/routing.py", line 66, in app
    response = await func(request)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/fastapi/routing.py", line 235, in app
    raw_response = await run_endpoint_function(
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/fastapi/routing.py", line 163, in run_endpoint_function
    return await run_in_threadpool(dependant.call, **values)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/starlette/concurrency.py", line 41, in run_in_threadpool
    return await anyio.to_thread.run_sync(func, *args)
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/anyio/to_thread.py", line 31, in run_sync
    return await get_asynclib().run_sync_in_worker_thread(
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/anyio/_backends/_asyncio.py", line 937, in run_sync_in_worker_thread
    return await future
  File "/Users/abcB/Desktop/fastapi-tutorial/env/lib/python3.9/site-packages/anyio/_backends/_asyncio.py", line 867, in run
    result = context.run(func, *args)
  File "/Users/abcB/Desktop/fastapi-tutorial/./main.py", line 31, in get_person
    return people[person_id]

问题排查与解决方案 #

核心问题 #

错误回溯最后一行显示return people[person_id]触发异常，原因是：

• people字典使用字符串类型的键（"1"、"2"）
• 接口参数person_id声明为int类型，FastAPI会自动将URL中的路径参数解析为int
• 用int类型的键查找字符串键的字典，会直接抛出KeyError，导致500内部服务器错误

两种修复方案 #

方案1：修改参数类型为字符串

将get_person函数的参数类型改为str，匹配字典的键类型：

@app.get("/people/{person_id}")
def get_person(person_id: str): 
    return people[person_id]

方案2：修改字典的键为整数

调整people字典的键为int类型，和参数类型保持一致：

people = {
    1: {
        "name": "abc", 
        "age": 27
    }, 
    2: {
        "name": "xyz", 
        "age": 60
    }
}

额外优化：处理不存在的ID #

为了避免用户传入不存在的ID时仍返回500错误，可以添加异常处理，返回更友好的404响应：

from fastapi import FastAPI, HTTPException

# ... 其他代码 ...

@app.get("/people/{person_id}")
def get_person(person_id: str): 
    person = people.get(person_id)
    if not person:
        raise HTTPException(status_code=404, detail="Person not found")
    return person

内容的提问来源于stack exchange，提问作者Alwaysblue