Template Engines¶

We introduce in this page the basics of Jinja2 syntax used by templating on our platform. The reader is referred to the official documentations for further information ¹².

Basic Syntax¶

The general convention of the syntax ³:

{% ... %}: for Statements
{{ ... }}: for Expressions to print to the template output
{# ... #}: for Commentaries not included in the template output

Variables Assignment¶

Inside code blocks, the user can also assign values to variables using the "set" statement, such as in the following example, where element_name is the variable name and "Al" represents its assigned value.

{% set element_name = "Al" %}

Inserting Variables¶

The following simple example illustrates the basic syntax for inserting variables, based on the use of pairs of curly braces mentioned above.

{{name}} has the chemical formula {{formula}}.

If name="Silica" and formula="SiO2", then the templating engine will generate, or render, the following final output after acting upon the above template input.

Silica has the chemical formula SiO2.

Accessing Context Nested Keys¶

The bracket notation is employed for accessing keys from different levels across a nested context. For example, in the case of the nested context shown below, the KPPRA variable would be imported from its parent keyword "kgrid" as shown in the ensuing line.

{
    "kgrid": {
        "KPPRA": 32000,
    }
}

KPPRA =  {{ kgrid["KPPRA"] }}

Dot Notation

For the template variables rendered at design time one can use Javascript "dot notation" to access a nested key.

KPPRA =  {{ kgrid.KPPRA }}

The input variable definitions and associated values are provided in the Context of the template.

Loops and Conditional Statements¶

Control structures such as Loops and Conditional Statements can control the flow of the template. Here, we cover conditionals and for-loops by way of examples.

Conditionals¶

A basic conditional "if/else" type of statement in Jinja would consist in the following block of statements.

{% if truth_value %}
This is true
{% else %}
This is false
{% endif %}

If boolean truth_value resolves to true, then the output of the above template will be This is true and vice versa.

Loops¶

We now create a template containing a "for" loop, as in the following example.

{% for element in elements %}
{{ element }}
{% endfor %}

If elements = ['Bi', 'O', 'Cu'], then the following output is rendered.

    Bi

    O

    Cu

Filters¶

Template variables can be modified by filters. Filters are separated from the variable by a pipe symbol (|), and may have optional arguments passed to them in parentheses. Multiple filters can also be chained, meaning that the output of one filter is applied to the next.

Supported Jinja2 built-in filters are reviewed in its documentation web-page ⁴.