Flask and sys.excepthook
Flask already handles exceptions in views for you. Using sys.excepthook is not the right way to handle this, the hook will never be called.
Specify a custom exception handler with Flask instead, see the Redirects and Errors section of the Quickstart manual:
from flask import render_template@app.errorhandler(500)def page_not_found(error): return 'some error message'Flask also uses the logging module to record exceptions; configure the logging module to write anything of severity logging.ERROR to the console or a log file.
Since you use app.run(debug=True, port=5001), you'll already see exceptions printed to the console.
Note that the 500 error page is only ever invoked when debug is not set to True however; otherwise the Werkzeug debug view is invoked instead.