Hops can be best compared by external modules in programming. First you create a script, which works similarly to a cluster. After that you add a hop which references to your created definition. Hops can also be used to run external Python scripts in Grasshopper while letting you write them in a code editor which allows you to use debugging tools. We will show both examples in this tutorial.

Grasshopper Hops 1/8

Why Hopslink copied

When your knowledge about building Grasshopper scripts is increasing, it is easy to lose the control over your script because of its size. Grasshopper gives users several methods to make it easier to get an overview of what you made. Furthermore, some of these techniques can be used to publish, share and optimize your scripts. Generally speaking, there are three options:

• Group your components;
• Cluster components;
• Hops.

This tutorial goes into the usages of hops. There are two main ways to use hops:

• To incorporate definitions into components that we call clusters
• To run scrips in Gasshopper that were created in a code editor

When using hops, there are several advantages and disadvantages to consider. 

Advantages

• Hops can be computed parallel and therefore can be efficient in complex definitions;
• Hops can cache solutions to use again;
• Hops can use multiple processor cores in calculations;
•  Hops can be executed using the GrasshopperPlayer function in Rhino;
• Hops can use plugins from Grasshopper, like ladybug, anemone etc. as long as you have installed them.

Disadvantages

• Hops may take more time to calculate initially;
• Hops have less available input types. Vectors for example, are not available. Currently, McNeel advices to convert these datatypes to strings first (April, 2024);
• Nested hops are currently not possible;
• You cannot directly see a script when double-clicking on a hop, which makes it less traceable.

Grasshopper Hops 2/8

Installing Hopslink copied

First we need to install the Hop module. Open the Package Manager in Rhino and search for Hops. Install the latest version available. You will have to restart Grasshopper to use the plugin.
 

• Open the Package Manager Rhino » Tools » Package Manager
• Type and install Hops
• Restart Rhino and Grasshopper

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Hops for Clusters (Hopable Definitions)link copied

A key part of creating a Hopable Definition is defining the input and outputs of the component. To do this, there are specific Hops components you can use.

Instead of using standard Grasshopper input Parameters and Number Sliders, you will have to use the Hops contextual parameters in your script to create an input. Contextual Parameters can be found in the Util tab under Params. These components, will create the input field in your component. You can only have a Hops-supported input which means some input options are limited.

Inputs

• Replace all inputs with contextual parameters Params » Util

Outputs

To create an output, you use standard Grasshopper components from the Geometry and Primitive toolbars. Use the same type as the data you create. First, place and connect the correct Geometry or Primitive component, select it, and group it. Next, rename the group to RH_OUT:[output name]. You can output multiple objects by adding multiple groups.

• Output the correct data Select output nodes » RMB on canvas » Group » RMB on group » Rename to RH_OUT:[output name]

Optional: Bake Output

Optionally, by adding the Contextual Bake component at the end of your script, the output of the script will be baked automatically when it is finished calculating.

•  Add a contextual bake component at the end of your script Params » Util » Contextual Bake

Save Script

• Save your definition GH Menu » Save document as

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Running a Hopable Scriptlink copied

Open an empty canvas in Grasshopper and add the Hops component to the canvas.

Running Hops in Rhino

It is also possible to use your Hop definition using the Rhino Command Line. 

Grasshopper Hops 5/8

Overview of Using Hops to run Python Scriptslink copied

Hops can also be used to run Python scripts that are written outside of Grasshopper. In the past, the Python component in Grasshopper did not have the same support tools that working in a code editor does, for example it did not have a debugger (a tool that notices and marks mistakes in your script). It also did not support importing external libraries like Numpy and Scipy. 

When the Script component was introduced, it alleviated some of these problems. For example you can now use Python 3 to write your code and you can import external libraries. However, the Script component still has some drawbacks. Running a Python script in the Script component can be slow, especially when handling large datasets and complex geometry. Additionally, there are still limitations on debugging your code. This is when Hops can be helpful. Hops allows you to run Python (and other scripts) outside of Grasshopper. This means the code will execute faster since it runs on an external server or environment and you get the benefits of debugging tools.

The Script component is a big improvement for running Python code in Grasshopper, but when you need to execute code quickly or want access to a full range of debugging tools, writing a Python script in a code editor like VS code and linking it with Hops may be a more appropriate option.
In addition to the information provided below, you can also reference the Rhino Developer guide on Hops at https://developer.rhino3d.com/guides/compute/hops-component/.

Getting Started

To learn how to install Hops, reference the previous section of the tutorial.

When using Hops to run a Python script you also need to use a code editor to write your Python code. Some options include VS Code (Visual Studio Code – Code Editing. Redefined) and PyCharm (PyCharm: The Python IDE for data science and web development by JetBrains).

The Hops Server

Hops uses flask and the ghhops-server libraries so you will need to install both in your development environment.

pip install flask
pip install ghhops-server

Writing Your Code

When writing the code for a component you need to follow the structure required and documented for Hops components. You can find the documentation on GitHub (https://github.com/mcneel/compute.rhino3d/tree/8.x/src/ghhops-server-py).

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Creating a Python Script for Hopslink copied

We are going to create a script to calculate the Pythagoras Formula like we did in the example earlier. This time, however we will use Python to write a script and then use Hops to run this script.

First, import the dependencies. 

from flask import Flask
import ghhops_server as hs
import math

Then register the Hops application as middleware. Starting with the @hops.component decorate, decorate the function. The first argument passed to the decorator (“/pythagorasformula “) is the URL of this component on our server you will need this to link the Python code into Grasshopper. In this example, we will name the function pythagorasformula, we have two inputs (a and b) and one output (c). 

# register hops app as middleware
app = Flask(__name__)
hops = hs.Hops(app)

@hops.component(
    "/pythagorasformula",
    name="PythagorasFormula",
    description="with 2 inputs, solves Pythagoras' Formula",
    inputs=[
        hs.HopsNumber("a", "a", "the first number in the formula"),
        hs.HopsNumber("b", "b", "the second number in the formula"),
    ],
    outputs=[
        hs.HopsNumber("c", "c", "the output of the formula")
    ]
)
def pythagorasformula(a, b):
    c = math.sqrt(a**2 + b**2)
    return c

If you are defining multiple Hops components, you can continue by declaring a new decorator and then writing your next function. 

Finally, end the script by running the Hops server.

if __name__ == "__main__":
    app.run()

Save the code to a file called app.py in the python file, navigate to the file location in your terminal, and run it using python:

Python app.py

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Running a Python Script in Hopslink copied

You will continue in grasshopper. Open an empty canvas in Grasshopper and add the Hops component to the canvas.

Grasshopper Hops 8/8

Conclusionlink copied

Through this tutorial you learned how to use Hops to cluster components which also allows you to use all of the options Hops offers like parallel computing. You also reviewed how Hops can be used to run Python code that you create using a code editor for when need to execute code quickly or want access to a full range of debugging tools.

Useful links

VS Code (Visual Studio Code – Code Editing. Redefined)

PyCharm (PyCharm: The Python IDE for data science and web development by JetBrains)

Rhino Compute Server documentation on GitHub (https://github.com/mcneel/compute.rhino3d/tree/8.x/src/ghhops-server-py)