Flask App Running: Command Line or Python Script? Which Should You Choose?

Running Flask Applications: Flask Command vs. Python Script

The documentation for Flask lists two methods to start an application: using the flask command or running a Python script. While both achieve the same result, there are significant differences to consider when selecting one over the other.

Flask Command

The flask command is the recommended option for running Flask applications, particularly during development. It provides a command-line interface for interacting with Flask apps, allowing you to perform tasks such as running the development server or deploying the application. To start the development server using the flask command, use:

$ flask --app sample --debug run

The --app option specifies the name of the module or path to the app instance. The --debug option enables debug mode, which provides additional information and tools during development.

Python Script

Running a Flask application as a Python script involves executing the main module of the application, typically identified as app.py. Within the script, the app.run() function is used to start the development server.

if __name__ == "__main__":
    app = create_app()
    app.run(debug=True)

In this example, create_app() instantiates the Flask application, and app.run(debug=True) starts the development server with debug mode enabled.

Key Differences

The flask command offers several advantages over the Python script approach:

• Customization: The flask command allows developers to add custom commands to their applications.
• Configuration: The flask command automatically detects and loads the configuration settings defined in the app instance.
• Environment: The flask command sets the application environment to "development" by default, enabling the reloader and debugger.
• Cross-Platform: The flask command is a cross-platform tool that works on Linux, Windows, and macOS.

When to Use Each Method

Flask Command: Use the flask command during development to:

• Execute the application's main module.
• Start the development server with debug mode enabled.
• Customize and extend the command-line interface.

Python Script: Use a Python script to run the application in situations where:

• The flask command is not available.
• You require custom initialization or configuration logic outside the scope of the flask command.

While both methods can achieve the same result, the flask command is the preferred choice for development purposes due to its ease of use, customization capabilities, and optimized configuration for Flask applications.

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