Flask tutorial - 404 Not Found

You put your app.run() call too early:

if __name__== '__main__':
    app.run()

This is executed before any of your routes are registered. Move these two lines to the end of your file.

Next, you have the first line in show_entries() is incorrect:

def show_entries():
    db_get_db()

There is no db_get_db() function; this should be db = get_db() instead.

Happened to me also while following Flask Application Setup here . The error was gone after appending a trailing slash at the end of the route.

@app.route('/hello')
    def hello():
        return 'Hello, World!'

was changed to

@app.route('/hello/')
    def hello():
        return 'Hello, World!'

and the problem was solved. Hope it helps for anyone who is searching for a problem like this.