Control structures

In Jinja2, a control structure refers to things in a template that control the flow of the engine parsing the template. These structures include, but are not limited to, conditionals, loops, and macros. Within Jinja2 (assuming the defaults are in use), a control structure will appear inside blocks of {% … %}. These opening and closing blocks alert the Jinja2 parser that a control statement is provided instead of a normal string or variable name.

Conditionals

A conditional within a template creates a decision path. The engine will consider the conditional and choose from two or more potential blocks of code. There is always a minimum of two: a path if the conditional is met (evaluated as true), and an implied else path of an empty block.

The statement for conditionals is the if statement. This statement works much like it does in Python. An if statement can be combined with one or more optional elif with an optional final else, and unlike Python, requires an explicit...