# Family Parameters

Revit's family system uses a hierarchical relationship between Family Types and Family Instances. The same relationship exists in parallel in the API:

* Placed family instances (e.g. a window or a window) are instance of Revit's [FamilyInstance](https://apidocs.co/apps/revit/2019/ea6bc434-d938-d0e5-ecc3-33e37dbf1d1b.htm) class.
* Family Types (e.g. 90 minute fire-rated door type) are instances of Revit's [FamilyType](https://apidocs.co/apps/revit/2019/e57e8440-14b8-5f33-e014-5fcae26f244a.htm) class.

#### Family Instance vs Family Type Parameters

It is worth understanding a simple fact about family parameters:

*A family's instance parameters are accessed via the FamilyInstance object, whereas family type parameters are accessed via the instance's FamilyType object.*

Using a few simple methods, you can move from a family instance's FamilyInstance to its associated FamilyType, and from that FamilyType to the associated Family. We can also carry out the movements in reverse, finding all Family Types of a Family, or all placed instances of a Family Type. To make things clearer, we've put this on its own page:

{% content-ref url="/pages/-LsmOf578RTQNnBT-Q8v" %}
[4.13 Family Acrobatics](/dynamo-python-primer/4-revit-specific-topics/family-acrobatics.md)
{% endcontent-ref %}

#### Seeing All Family Instance Parameters

As ever, if wanting to interact with a Revit element passed into a node, it will need to be unwrapped. See how to unwrap elements here: [Unwrapping Revit Elements](/dynamo-python-primer/4-revit-specific-topics/unwrapping-revit-elements.md)

Once unwrapped, you can either access a particular parameter (see section on Accessing a Specific Parameter below) or return a list of all the element's instance parameters as [Parameter](https://apidocs.co/apps/revit/2019/c0343d88-ea6f-f718-2828-7970c15e4a9e.htm) objects, which can be accessed via its Element.Parameters property, like so:

```python
#Boilerplate Code
my_element = UnwrapElement(IN[0])
element_parameters = my_element.Parameters
```

This is akin to using the Element.Parameters node on in Dynamo. Now we have the list of Parameter objects, we can do many things. Looking at the [Parameter](https://apidocs.co/apps/revit/2019/c0343d88-ea6f-f718-2828-7970c15e4a9e.htm) class in ApiDocs.co, we can see there are a number of useful properties we can inspect.

#### Seeing All Family Type Parameters

Type Parameters need to be accessed via an element’s family type. If you have a [FamilyInstance](https://apidocs.co/apps/revit/2019/0d2231f8-91e6-794f-92ae-16aad8014b27.htm) as an input, you’ll firstly need to use an intermediate method to get the element’s [FamilyType](https://apidocs.co/apps/revit/2019/7f15b213-c99b-db59-3622-3280757b82d9.htm) object, such as GetTypeId().

This method returns the [ElementId](https://apidocs.co/apps/revit/2019/44f3f7b1-3229-3404-93c9-dc5e70337dd6.htm) of the element’s family type. We can then use the doc.GetElement() method to return the element’s FamilyType object. We can assign a reference to the family type, such as:

```python
family_type = doc.GetElement(family_instance.GetTypeId())
```

The family\_type handle is now a way to access the family type object. We can then go about accessing parameters using the methods below.

#### Accessing a Specific Parameter

Once we've placed a handle to our FamilyInstance or FamilyType, there are a couple of different ways to access a particular parameter:

* The Element.LookupParameter() method.
* The Element.get\_Parameter() method.

Both of these methods essentially do the same thing; they return a Parameter object which you can inspect and manipulate.

![A simple example; reading the Mark value of an element.](/files/-LsmJCHVJYQreHcRoF8V)

#### Reading A Parameter's Value

Finally, in order to read a parameter object’s value, you’ll need to convert it using one of the methods of the Parameter class, such as .AsString() or .AsDouble().\
\
If you output the raw Parameter object, it shows as **Autodesk.Revit.DB.Parameter** which isn't very helpful. Use the methods above to return the value in an appropriate data type. This workflow is the equivalent of using the GetParameterValueByName node in Dynamo.


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