How to Download A File Using Fastapi?

To download a file using FastAPI, you can create an endpoint that returns a FileResponse object from the Starlette library. First, you need to import the necessary modules:

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from fastapi import FastAPI
from starlette.responses import FileResponse

Then, create a FastAPI app instance:

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app = FastAPI()

Next, define a route that returns a file:

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@app.get("/download-file")
async def download_file():
    file_path = "path/to/your/file.txt"
    return FileResponse(file_path)

In the example above, the download_file endpoint returns the file at "path/to/your/file.txt" when accessed. You can customize the file path and endpoint URL per your requirement.

To test the endpoint, run the FastAPI app using:

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uvicorn your_app_name:app --reload

Navigate to http://localhost:8000/download-file in your browser, and the file will be downloaded automatically.

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How to return JSON responses in FastAPI?

To return JSON responses in FastAPI, you can simply create a dictionary with the data you want to return and then return it using FastAPI's Response class or by using FastAPI's JSONResponse class.

Here is an example of how you can return a JSON response in FastAPI:

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from fastapi import FastAPI
from fastapi.responses import JSONResponse

app = FastAPI()

@app.get("/json")
def read_json():
    data = {"message": "Hello, World!"}
    return JSONResponse(content=data)

In this example, the /json endpoint will return a JSON response with the data {"message": "Hello, World!"}.

You can also use FastAPI's Response class to return JSON responses:

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from fastapi import FastAPI, Response
import json

app = FastAPI()

@app.get("/json")
def read_json():
    data = {"message": "Hello, World!"}
    return Response(content=json.dumps(data), media_type="application/json")

In this example, we are using the Response class to return a JSON response with the data {"message": "Hello, World!"}.

Both of these methods will return a JSON response in FastAPI.

How to handle exceptions in FastAPI?

In FastAPI, you can handle exceptions by defining custom exception handlers. Here's how you can handle exceptions in FastAPI:

1. Create a custom exception handler function:

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from fastapi import FastAPI, HTTPException

app = FastAPI()

@app.exception_handler(HTTPException)
async def http_exception_handler(request, exc):
    return JSONResponse(
        status_code=exc.status_code,
        content={"message": exc.detail},
    )

1. Decorate your endpoint function with the @app.get() or @app.post() decorator:

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@app.get("/items/{item_id}")
async def read_item(item_id: int):
    if item_id == 0:
        raise HTTPException(status_code=400, detail="Item ID must be greater than 0")
    return {"item_id": item_id}

In this example, if the item_id is equal to 0, we raise an HTTPException with a status code of 400 and a custom error message.

1. Register the custom exception handler function in your FastAPI app:

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app.add_exception_handler(HTTPException, http_exception_handler)

Now, whenever an HTTPException is raised in your application, FastAPI will call the http_exception_handler function to handle the exception and return a custom error response.

By following these steps, you can handle exceptions in FastAPI and customize the error responses returned to clients.

What is FastAPI's relationship with Starlette?

FastAPI is built on top of Starlette, which is a lightweight ASGI framework for building web applications. FastAPI uses Starlette's capabilities to handle requests and responses, allowing for high performance and efficient handling of asynchronous tasks. This relationship helps FastAPI provide quick and efficient web application development while leveraging the features and capabilities of Starlette.

How to log messages in FastAPI?

In FastAPI, you can log messages using the standard Python logging library. Here is an example of how to set up logging in FastAPI:

1. Import the logging library:

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import logging

1. Configure the logging settings in your FastAPI application, for example in the main.py file:

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logging.basicConfig(level=logging.INFO)

1. Add logging calls in your FastAPI application where needed. For example, you can use logging.debug, logging.info, logging.warning, logging.error, and logging.critical functions to log messages with different logging levels:

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logging.info("This is an info message")
logging.error("This is an error message")

1. To see the logs when running your FastAPI application, you can use the uvicorn command with the --reload flag to start the server in development mode, which will display the logs in the terminal:

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uvicorn main:app --reload

Logs will be displayed in the console with the corresponding logging levels and messages. You can also configure additional settings like log file paths, formatting, and handlers according to your requirements.