Fixing CORS in FastAPI Python: A Step-by-Step Guide

CORS (Cross-Origin Resource Sharing) is a security feature implemented in web browsers to prevent unauthorized access to resources on different origins. This is a common issue when developing web applications, especially when using APIs. In this article, we will discuss how to fix CORS in FastAPI, a modern, fast (high-performance), web framework for building APIs with Python 3.7+.

When building an API with FastAPI, you may encounter CORS-related errors when making requests from a different origin than the one that serves the API. This is a common issue when developing frontend applications that need to access APIs from a different domain.

To fix CORS in FastAPI, you can use the fastapi.middleware.cors middleware to allow cross-origin requests. Here’s a step-by-step guide to enable CORS in your FastAPI application:

Step 1: Install the required packages
“`
pip install fastapi
pip install uvicorn
“`

Step 2: Import the necessary modules in your Python file
“`html
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
“`

Step 3: Create an instance of the FastAPI application
“`html
app = FastAPI()
“`

Step 4: Add the CORSMiddleware to the FastAPI application
“`html
app.add_middleware(
CORSMiddleware,
allow_origins=[“*”],
allow_credentials=True,
allow_methods=[“*”],
allow_headers=[“*”],
)
“`

In the above code, we add the CORSMiddleware to the FastAPI application and configure it to allow all origins (“*”), credentials, methods, and headers. You can customize these settings according to your specific requirements.

Step 5: Run the FastAPI application using uvicorn
“`html
uvicorn your_module_name:app –reload
“`

Replace “your_module_name” with the name of your Python file.

With the above steps, you have successfully fixed CORS in your FastAPI application. Now, your API should be accessible from different origins without any CORS-related errors.

In conclusion, fixing CORS in FastAPI is a straightforward process that involves adding the CORSMiddleware to the application and configuring it to allow cross-origin requests. By following the steps outlined in this article, you can ensure that your FastAPI application is accessible from different origins while maintaining the necessary security measures.