Tip: Jinja2 Macros

Cylc Tips
1

Jinja2 macros are great way to automatically construct parts of your workflow based on input parameters (macro arguments).

Here’s an example macro that adds a task to print a given word (default “hello”) to stdout, after a given task in your graph:

{% macro say_it(
        after_task,
        say_what = "hello"
    )
%}
[scheduling]
    [[graph]]
        R1 = "{{after_task}} => say_{{say_what}}"
[runtime]
    [[say_{{say_what}}]]
        script = "echo {{say_what}}"
{% endmacro %}

And a workflow that uses it twice:

#!Jinja2
{% import 'macros.j2' as macros %}

{{ macros.say_it(after_task="b")}}
{{ macros.say_it(after_task="c", say_what="goodbye")}}
[scheduling]
    [[graph]]
        R1 = "a => b => c"
[runtime]
    [[a, b, c]]

Here’s the result after template processing and config parsing, via cylc config:

[scheduling]
    initial cycle point = 1
    final cycle point = 1
    cycling mode = integer
    [[graph]]
        R1 = """
            b => say_hello
            c => say_goodbye
            a => b => c
        """
[runtime]
    [[root]]
    [[say_hello]]
        script = echo hello
        completion = succeeded
    [[say_goodbye]]
        script = echo goodbye
        completion = succeeded
    [[a]]
        completion = succeeded
    [[b]]
        completion = succeeded
    [[c]]
        completion = succeeded
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