Returns a Placeholder that represents an execution property.

key The key of the output artifact.

A Placeholder that supports

  1. Rendering the value of an execution property at a given key. Example: exec_property('version')
  2. Rendering the whole proto or a proto field of an execution property, if the value is a proto type. The (possibly nested) proto field in a placeholder can be accessed as if accessing a proto field in Python. Example: exec_property('model_config').num_layers
  3. Concatenating with other placeholders or strings. Example: output('model').uri + '/model/' + exec_property('version')