## Plugin.match

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

Source | Added |
---|---|

Link | 1.4.3 |

### Introduction

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.

- Intersection
- Subset
- 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"])
```

### Usage

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

**Example**

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 instance.data["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
```