Скачать или смотреть How to Run a Flask App with python app.py Instead of flask run

Discover how to properly run your Flask app using `python app.py` and troubleshoot common issues that may arise with URL not found errors.
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This video is based on the question https://stackoverflow.com/q/63712733/ asked by the user 'Ahmad_R' ( https://stackoverflow.com/u/2251348/ ) and on the answer https://stackoverflow.com/a/63713072/ provided by the user 'Seyi Daniel' ( https://stackoverflow.com/u/13505098/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting Your Flask App: Running with python app.py

If you're diving into web development with Flask and find yourself on a quest to run your app using python app.py rather than the conventional flask run, you're not alone. This common scenario can lead to confusion, especially when facing issues like getting a "requested URL not found" error. In this guide, we will explain the problem and guide you step-by-step to a solution that ensures your Flask app runs smoothly.

The Problem: URL Not Found Error

When you attempt to execute your Flask application by running python app.py, an error can arise saying the URL is not found, even though your app runs perfectly with the flask run command. This can be the source of many frustrations, but the root cause usually lies in how the application is being structured and executed.

Understanding the Flask Application Structure

In a typical Flask app, the core components you need to know are:

Flask instance: This is created via app = Flask(__name__).

Routes: These define the endpoints for your web pages (the URLs users will visit).

Entry Point: Usually defined with if _name_ == "__main__":, which tells Python to run the app only when the script is executed directly.

The Solution: Properly Structuring Your Flask App

To successfully run your Flask app via python app.py, you'll need to ensure that the routing is correctly established before you initiate the app. Below is the revised and properly structured code you should use:

[[See Video to Reveal this Text or Code Snippet]]

Step-by-Step Breakdown

Import Necessary Libraries: Always ensure you import Flask and the necessary functions at the top of your file.

Create the Flask Instance: Declaring the Flask app using app = Flask(__name__) allows your application to recognize its identity.

Define the Routes: Place your route declarations (like @ app.route('/')) after defining the app instance but before the entry point. This ensures your routes are recognized when the application runs.

Entry Point Definition: Use the if _name_ == "__main__": block to run the application. The debug=True argument will help in displaying error messages in the browser, making it easier for you to debug any potential issues.

Conclusion

Running your Flask app using python app.py can be straightforward, provided that your code is structured correctly. By following the steps outlined above and ensuring that your routes are defined before launching the app, you should be able to resolve the URL not found errors. Happy coding!