Web frameworks
The MVC pattern
A very simple application
Application of the MVC pattern
Making a Flask application
Programming the Flask application
Equipping the input page with output results
Splitting the app into model, view, and controller files
Troubleshooting
Handling multiple input variables in Flask
Programming the Flask application
Implementing error checking in the template
Using style sheets
Using LaTeX mathematics
Rearringing the elements in the HTML template
User-provided validation
Autogenerating the code
Avoiding plot files
PNG plots
SVG plots
Further work
Exercises
Exercise 1: Add two numbers
Exercise 2: Extend the vib3_flask app
Exercise 3: Equip the vib3_flask app with more data types
Exercise 4: Auto-generate code from function signature
Flask resources
Remaining
Computational scientists may want to offer their applications through a web interface, thereby making a web application. Basically, this means that users can set input data to the application on a web page, then click on some Compute button, and back comes a new web page with the results of the computations. The web interface can either be used as a GUI locally on the scientist's computer, or the interface can be depolyed to a server and made available to the whole world.
Web applications of the mentioned type can be created from scratch using CGI scripts in (e.g.) Python, but the code quickly gets longer and more involved as the complexity of the web interface grows. Nowadays, most web applications are created with the aid of web frameworks, which are software packages that simplify the programming tasks of offering services through the Internet. The downside of web frameworks is that there is a significant amount of steps and details to learn before your first simple demo application works. The upside is that advanced applications are within reach, without an overwhelming amount of programming, as soon as you have understood the basic demos.
We shall in the forthcoming text explore the very easy-to-use Flask framework. At the time of this writing, the primary Flask documentation is the official web site and the WTForms Documentation. That is why we have made specific examples for the application of Flask in computational science.
The problem for a computational scientist who wants to enable mathematical calculations through the web is that most of the introductory examples on utilizing a particular web framework address web applications of very different nature, e.g., blogs and polls. Therefore, we have made an alternative introduction which explains, in the simplest possible way, how web frameworks can be used to