# 4.7 Working With Parameters

**Working With Parameters**

There are a few different ways to set up parameters in Revit and each of them has a corresponding different way of being accessed.

* Shared parameters (defined in a .txt file)
* Project parameters (defined in a .rvt file)
* Family parameters (defined in a .rfa file)
* BuiltInParameters (hard-baked into the Revit software itself)

Shared, Project and Family parameters are known as '**custom parameters**' as users can define them as they wish; we'll look at [BuiltInParameters](/dynamo-python-primer/4-revit-specific-topics/working-with-parameters/built-in-parameters.md) separately. Each kind of custom parameter has a different way of being accessed within a project. 

* Global parameters (accessible everywhere throughout the file)
* Family Instance and Family Type parameters (accessible via a family type or a family instance)
* Project Information parameters (accessed via the project information dialog)
* Group parameters (accessed through a group definition or a group instance)

Finally, custom parameters can be made category-specific, so they might only be valid for Revit categories (e.g. a parameter that only applies to sheets).

#### Identifying Which Is Which

To get started with accessing a parameter using code, we’ll first need to identify which sort of parameter you’re wanting to access. Follow these steps to figure out what you're working with:

1. Does the parameter appear in the Properties Window when you click on a Revit family instance? This means it is an [instance parameter](/dynamo-python-primer/4-revit-specific-topics/working-with-parameters/instance-parameters.md).
2. If not visible in the Properties Window, does it appear when you click on the family and open the 'Edit Type' window? If so, then it's a [type parameter](/dynamo-python-primer/4-revit-specific-topics/working-with-parameters/instance-parameters.md).
3. Does the parameter appear in the Manage > Global Parameters dialog? If so, it's a global parameter and there are [special ways to access this](/dynamo-python-primer/4-revit-specific-topics/working-with-parameters/global-parameters.md). 
4. If the parameters appears in the Manage > Project Information parameter, there's a [special way to access this](/dynamo-python-primer/4-revit-specific-topics/working-with-parameters/project-information-parameters.md), too.
5. Does the parameter appear in the Properties Window when you click on a model or detail group? This means it is a [group instance parameter](/dynamo-python-primer/4-revit-specific-topics/working-with-parameters/group-parameters.md).
6. If not visible in the Properties Window, does it appear when you click on the group and open the 'Edit Type' window? Then it's a [group type parameter](/dynamo-python-primer/4-revit-specific-topics/working-with-parameters/group-parameters.md).

#### RevitLookUp

Another great way to understand which kind of parameter you're dealing with is to use the free [RevitLookUp](https://thebuildingcoder.typepad.com/blog/revitlookup/) addin for Revit. This lets you read (almost) every visible and invisible value for any Revit element. 

To make installing RevitLookUp easier, [Harry Mattison](https://twitter.com/boostyourbim?lang=en) (of the [BoostYourBIM blog](https://boostyourbim.wordpress.com/)) has put together Windows installers, which can be found [here](https://boostyourbim.wordpress.com/2018/05/17/revit-lookup-2019-installer/).


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