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Refer to Starlark function specification for details about various types of function arguments. Note that ytt’s Starlark use requires functions to be closed with an end.

  • function definition within YAML

Labels returns map with two keys: test1, and test2:

#@ def my_labels():
test1: 123
test2: 124
#@ end

Above is almost equivalent to (differnce is that return type in one case is a YAML fragment and in another it’s a dict):

#@ def my_labels():
#@   return {"test1": 123, "test2": 124}
#@ end
  • function definition within Starlark (.star files)
def my_labels():
  return {"test1": 123, "test2": 124}
  • function arguments (positional and keyword arguments)
#@ def my_deployment(name, replicas=1, labels={}):
kind: Deployment
  name: #@ name
  labels: #@ labels
  replicas: #@ replicas
#@ end

kind: List
- #@ my_deployment("dep1", replicas=3)
  • common function usage

To set labels key to return value of my_labels():

labels: #@ my_labels()
- #@ my_labels()

To merge return value of my_labels() into labels map:

#@ load("@ytt:template", "template")

  another-label: true
  _: #@ template.replace(my_labels())

Note that in most cases template.replace is not necessary since it’s only helps replacing one item (array item, map item or document) with multiple items of that type.