How Can I Effectively Debug and Handle Errors in My Flask Application?

How to Handle Errors in Flask: A Comprehensive Guide

Debugging errors in Flask requires a systematic approach to pinpoint the root cause. Print statements and flash messages offer basic troubleshooting, but Flask provides a more powerful tool: debug mode.

Running Flask in Debug Mode

Enabling debug mode provides an interactive traceback and console in the browser upon errors. In Flask 2.2 and later, run this command:

$ flask --app example --debug run

In earlier versions, set the FLASK_ENV=development environment variable instead. You can also use FLASK_APP and FLASK_DEBUG=1.

Using a Debugger

IDE debuggers like PyCharm and VS Code allow you to step through the code using breakpoints. Configure the run configuration to point to a script calling app.run(debug=True, use_reloader=False).

Alternatively, you can use terminal debuggers like pdb or pudb by calling set_trace in the view where you want to start debugging.

Other Troubleshooting Tips

• Avoid using broad except blocks, as they may silence the error. Flask will automatically handle exceptions.
• Print tracebacks to the terminal even when not in debug mode.
• Use debug mode to determine the exact point where the error occurs.
• If the app.run() method is used, pass debug=True to enable debug mode.
• Use the pdb package if you prefer a terminal debugger.

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