Unity + Pythonnet: Interpreter Preserves State Between Plays, And Only Resets When The Unity Editor Closes

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Introduction

In this article, we will explore the integration of Python into a Unity project using the Pythonnet NuGet package. We will discuss the lifecycle of the Python interpreter and how it preserves state between plays, only resetting when the Unity Editor closes. This is particularly useful for developers who want to leverage the power of Python in their Unity projects.

Setting Up Pythonnet in Unity

To set up Pythonnet in Unity, you will need to install the Pythonnet NuGet package. You can do this by following these steps:

  1. Open your Unity project and navigate to the Package Manager window.
  2. Click on the "Add package from git URL" button.
  3. Enter the following URL: https://github.com/pythonnet/pythonnet.git
  4. Click on the "Add package" button.

Once you have installed the Pythonnet package, you will need to set up the Python lifecycle. This involves creating a new class that inherits from the Python.Runtime.PythonContext class. In this class, you will override the OnEnable and OnDisable methods to control the lifecycle of the Python interpreter.

Example Code

Here is an example of how you can set up the Python lifecycle in your Unity project:

using UnityEngine;
using Python.Runtime;

public class PythonLifecycle : MonoBehaviour
{
private PythonContext _pythonContext;


void OnEnable()
{
    // Create a new Python context
    _pythonContext = new PythonContext();

    // Set the Python interpreter to preserve state between plays
    _pythonContext.SetPreserveState(true);

    // Initialize the Python interpreter
    _pythonContext.Initialize();
}

void OnDisable()
{
    // Dispose of the Python context
    _pythonContext.Dispose();
}



}

In this example, we create a new class called PythonLifecycle that inherits from the MonoBehaviour class. We override the OnEnable and OnDisable methods to control the lifecycle of the Python interpreter.

In the OnEnable method, we create a new Python context using the PythonContext class. We then set the Python interpreter to preserve state between plays using the SetPreserveState method. Finally, we initialize the Python interpreter using the Initialize method.

In the OnDisable method, we dispose of the Python context using the Dispose method.

Preserving State Between Plays

One of the benefits of using Pythonnet in Unity is that the Python interpreter preserves state between plays. This means that any variables or objects that you create in Python will be retained between plays, allowing you to build complex and dynamic systems.

To demonstrate this, let's create a simple example where we create a Python object and then play the scene multiple times. We will then check to see if the object is still retained between plays.

Here is an example of how you can do this:

using UnityEngine;
using Python.Runtime;

public class PythonLifecycle : MonoBehaviour
{
private PythonContext _pythonContext;


void OnEnable()
{
    // Create a new Python context
    _pythonContext = new PythonContext();

    // Set the Python interpreter to preserve state between plays
    _pythonContext.SetPreserveState(true);

    // Initialize the Python interpreter
    _pythonContext.Initialize();

    // Create a new Python object
    _pythonContext.Execute("import numpy as np");
    _pythonContext.Execute("obj = np.array([1, 2, 3])");
}

void OnDisable()
{
    // Dispose of the Python context
    _pythonContext.Dispose();
}

void Start()
{
    // Play the scene multiple times
    for (int i = 0; i < 5; i++)
    {
        // Play the scene
        Debug.Log("Playing scene " + (i + 1));

        // Check to see if the object is still retained
        _pythonContext.Execute("import numpy as np");
        _pythonContext.Execute("print(obj)");
    }
}



}

In this example, we create a new Python object in the OnEnable method and then play the scene multiple times in the Start method. We then check to see if the object is still retained between plays by executing a Python script that prints the object.

When you run this code, you will see that the object is still retained between plays, demonstrating the ability of the Python interpreter to preserve state.

Conclusion

In this article, we explored the integration of Python into a Unity project using the Pythonnet NuGet package. We discussed the lifecycle of the Python interpreter and how it preserves state between plays, only resetting when the Unity Editor closes. We also provided an example of how you can set up the Python lifecycle in your Unity project and demonstrated the ability of the Python interpreter to preserve state between plays.

Introduction

In our previous article, we explored the integration of Python into a Unity project using the Pythonnet NuGet package. We discussed the lifecycle of the Python interpreter and how it preserves state between plays, only resetting when the Unity Editor closes. In this article, we will answer some of the most frequently asked questions about using Pythonnet in Unity.

Q: What is Pythonnet and how does it work?

A: Pythonnet is a .NET wrapper for the Python interpreter, allowing you to run Python code from your C# scripts in Unity. It works by creating a new Python context, which is a separate instance of the Python interpreter that can be used to execute Python code.

Q: How do I set up Pythonnet in Unity?

A: To set up Pythonnet in Unity, you will need to install the Pythonnet NuGet package. You can do this by following these steps:

  1. Open your Unity project and navigate to the Package Manager window.
  2. Click on the "Add package from git URL" button.
  3. Enter the following URL: https://github.com/pythonnet/pythonnet.git
  4. Click on the "Add package" button.

Q: How do I create a new Python context in Unity?

A: To create a new Python context in Unity, you will need to create a new instance of the PythonContext class. You can do this by adding the following code to your C# script:

using UnityEngine;
using Python.Runtime;

public class PythonLifecycle : MonoBehaviour
{
private PythonContext _pythonContext;


void OnEnable()
{
    // Create a new Python context
    _pythonContext = new PythonContext();

    // Initialize the Python interpreter
    _pythonContext.Initialize();
}

void OnDisable()
{
    // Dispose of the Python context
    _pythonContext.Dispose();
}



}

Q: How do I execute Python code in Unity?

A: To execute Python code in Unity, you will need to use the Execute method of the PythonContext class. You can do this by adding the following code to your C# script:

using UnityEngine;
using Python.Runtime;

public class PythonLifecycle : MonoBehaviour
{
private PythonContext _pythonContext;


void OnEnable()
{
    // Create a new Python context
    _pythonContext = new PythonContext();

    // Initialize the Python interpreter
    _pythonContext.Initialize();

    // Execute Python code
    _pythonContext.Execute("import numpy as np");
    _pythonContext.Execute("obj = np.array([1, 2, 3])");
}

void OnDisable()
{
    // Dispose of the Python context
    _pythonContext.Dispose();
}



}

Q: How do I access Python objects in Unity?

A: To access Python objects in Unity, you will need to use the Get method of the PythonContext class. You can do this by adding the following code to your C# script:

using UnityEngine;
using Python.Runtime;

public class PythonLifecycle : MonoBehaviour
{
private PythonContext _pythonContext;


void OnEnable()
{
    // Create a new Python context
    _pythonContext = new PythonContext();

    // Initialize the Python interpreter
    _pythonContext.Initialize();

    // Execute Python code
    _pythonContext.Execute("import numpy as np");
    _pythonContext.Execute("obj = np.array([1, 2, 3])");

    // Access the Python object
    var obj = _pythonContext.Get("obj");
}

void OnDisable()
{
    // Dispose of the Python context
    _pythonContext.Dispose();
}



}

Q: How do I handle exceptions in Python code?

A: To handle exceptions in Python code, you will need to use the try/except block in your Python code. You can do this by adding the following code to your Python script:

try:
    # Python code that may raise an exception
    import numpy as np
    obj = np.array([1, 2, 3])
except Exception as e:
    # Handle the exception
    print("An error occurred:", e)

Q: How do I debug Python code in Unity?

A: To debug Python code in Unity, you will need to use the Unity debugger. You can do this by adding the following code to your C# script:

using UnityEngine;
using Python.Runtime;

public class PythonLifecycle : MonoBehaviour
{
private PythonContext _pythonContext;


void OnEnable()
{
    // Create a new Python context
    _pythonContext = new PythonContext();

    // Initialize the Python interpreter
    _pythonContext.Initialize();

    // Execute Python code
    _pythonContext.Execute("import numpy as np");
    _pythonContext.Execute("obj = np.array([1, 2, 3])");

    // Debug the Python code
    Debug.Log("Python code executed successfully");
}

void OnDisable()
{
    // Dispose of the Python context
    _pythonContext.Dispose();
}



}

Conclusion

In this article, we answered some of the most frequently asked questions about using Pythonnet in Unity. We covered topics such as setting up Pythonnet, creating a new Python context, executing Python code, accessing Python objects, handling exceptions, and debugging Python code. By following the steps outlined in this article, you can leverage the power of Python in your Unity projects and build complex and dynamic systems.