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Response - Change Status Code


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You probably read before that you can set a default Response Status Code.

But in some cases you need to return a different status code than the default.

Use case

For example, imagine that you want to return an HTTP status code of "OK" 200 by default.

But if the data didn't exist, you want to create it, and return an HTTP status code of "CREATED" 201.

But you still want to be able to filter and convert the data you return with a response_model.

For those cases, you can use a Response parameter.

Use a Response parameter

You can declare a parameter of type Response in your path operation function (as you can do for cookies and headers).

And then you can set the status_code in that temporal response object.

from fastapi import FastAPI, Response, status

app = FastAPI()

tasks = {"foo": "Listen to the Bar Fighters"}

@app.put("/get-or-create-task/{task_id}", status_code=200)
def get_or_create_task(task_id: str, response: Response):
    if task_id not in tasks:
        tasks[task_id] = "This didn't exist before"
        response.status_code = status.HTTP_201_CREATED
    return tasks[task_id]

And then you can return any object you need, as you normally would (a dict, a database model, etc).

And if you declared a response_model, it will still be used to filter and convert the object you returned.

FastAPI will use that temporal response to extract the status code (also cookies and headers), and will put them in the final response that contains the value you returned, filtered by any response_model.

You can also declare the Response parameter in dependencies, and set the status code in them. But keep in mind that the last one to be set will win.