Control how families are matched amongst plug-ins and instances.

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Link 1.4.3


The way instances are associated with plug-ins are via their families.

Instances and plug-ins may support one or more families, and instances matching one or more of these families are said to be associated with it.

An instance may be associated via a plug-in in 1 of 3 ways.

  1. Intersection
  2. Subset
  3. Exact

By default, an instance of any family within the supported families of a plug-in is a match. This is called Intersection and stems from basic set theory.

assert set(["a", "b"]).intersection(["b", "c"])

This is useful in the most general case, of one plug-in supporting many different - possibly unrelated - families. Such as one plug-in supporting both models and rigs, say for an established naming convention across both families.

Subset on the other hand means the families of an Instance must be a subset of the supported families of any plug-in.

Again the concept is borrowed from set theory.

assert set(["a", "b"]).issubset(["a", "b", "c"])

This can be useful when instances are specialised, such as being a lowpoly family of a model, or animation family of a rig.

Finally, there is Exact which captures edge-cases or otherwise highly context sensitive instances, such as an animation rig in shot05.

The algorithm is as follows.

assert set(["a", "b"]) == set(["b", "a"])


Decide whether your plug-in targets many unrelated families, or specialises in a few, then associate an algorithm with this plug-in.


In this example, SpecificPlugin is associated to instances whose family(ies) are a subset of the supported families model and low. If the instance does not have at least both of these, it is not a match.

This is different from GenericPlugin, where only one of the families of an instance need to match any of the supported families of a plug-in. This is called intersection.

from pyblish import api

class GenericPlugin(api.InstancePlugin):
  # Support both models and rigs
  families = ["model", "rig"]

  def process(self, instance):
    # Applies to both models and rigs
    assert "parent_GRP" in instance

class SpecificPlugin(api.InstancePlugin):
  # Support models, but only low-poly models
  families = ["model", "low"]
  match = api.Subset

  def process(self, instance):
    # Safe to assume it has a `polyCount` due
    # to only capturing models.
    assert["polyCount"] < 500

The last possible value is Exact which means an instance only matches when families of both instance and plug-ins match exactly.

class EdgeCasePlugin(api.InstancePlugin):
  families = ["model", "low", "level21"]
  match = api.Exact

  def process(self, instance):
    assert "specialMember" in instance

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