How to Enable Cross-Origin Resource Sharing (CORS) in Flask Applications?

Enabling CORS in Flask

When performing cross-origin requests using jQuery, you may encounter errors related to missing 'Access-Control-Allow-Origin' headers. This occurs when the server has not explicitly allowed cross-origin requests. To resolve this issue in Flask, you can follow these steps:

1. Install Flask-CORS

Install the Flask-CORS extension using pip:

<code class="bash">pip install -U flask-cors</code>

2. Initialize and Configure Flask-CORS

Import the Flask-CORS package and initialize it in your Flask application:

<code class="python">from flask_cors import CORS
app = Flask(__name__)
cors = CORS(app)</code>

3. Set CORS Headers

Specify the allowed CORS headers in your Flask configuration:

<code class="python">app.config['CORS_HEADERS'] = 'Content-Type'</code>

4. Allow Cross-Origin Requests

Within your request handling methods, explicitly allow cross-origin requests using the @cross_origin() decorator:

<code class="python">@app.route("/")
@cross_origin()
def helloWorld():
  return "Hello, cross-origin-world!"</code>

5. Deploy to Heroku

Once the CORS configuration is in place, you can deploy your Flask application to Heroku.

Additional Notes

• The CORS_HEADERS configuration allows you to specify the headers that you want to expose for cross-origin requests.
• The @cross_origin() decorator allows you to selectively enable cross-origin requests for specific routes in your application.
• If you encounter any issues, refer to the Flask-CORS documentation for further guidance.

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