Chapter 3. The Template Language

While a programming language is designed to manipulate data, a presentation language is used to turn the data into plain text, HTML, or some other format.^[1] As long as the data is made available to us in a textual representation when we ask for it, we really don't need to worry too much about how it is stored or computed behind the scenes.

^[1] We'll assume for now that the presentation formats are all different kinds of text, although you can also use the Template Toolkit to generate binary files such as images.

That's not to say that you can't create and manipulate variables in templates. However, their most common use is for dealing only with presentation aspects, by using variables to define colors or other layout parameters, displaying the first N search results, or sorting a list of names into alphabetical order, for example. It is unusual (but not unheard of) to use the Template Toolkit to modify data that has any lasting effect. In general, data is passed to a template and then thrown away, so it doesn't matter if it's changed in any way.