Скачать или смотреть Troubleshooting Python Module Imports with pythonnet in Unity

Learn how to effectively load Python modules asynchronously in Unity using pythonnet, and discover common pitfalls and solutions when integrating Python threaded libraries.
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This video is based on the question https://stackoverflow.com/q/79471332/ asked by the user 'Micanroules' ( https://stackoverflow.com/u/29814546/ ) and on the answer https://stackoverflow.com/a/79481880/ provided by the user 'LOST' ( https://stackoverflow.com/u/231238/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

Integrating Python scripts into Unity projects using pythonnet allows leveraging powerful Python libraries directly. However, asynchronous loading of Python modules can sometimes cause unexpected behavior, especially with libraries relying on internal threading.

This post explores a common issue: when importing a Python module with internal libraries asynchronously, part of the module's functionality doesn't work as expected without errors.



The Core Problem

Using pythonnet in Unity, the first-time import of certain Python modules takes noticeable time.

To prevent blocking Unity's main thread, asynchronous import (Task.Run) alongside PythonEngine.BeginAllowThreads() was used.

While the main Python module imports successfully, one of its internal libraries behaves incorrectly.

Switching back to synchronous loading makes everything work fine.

This indicates the issue relates to thread management and Python runtime initialization during asynchronous imports.



Why Does This Happen?

Python’s threading and GIL (Global Interpreter Lock) management can be tricky when embedding Python in a multi-threaded environment like Unity:

pythonnet requires explicit GIL handling (Py.GIL()) when invoking Python code.

PythonEngine.BeginAllowThreads() is intended to enable Python threading from C# threads.

Some Python modules (especially those with internal threads or asynchronous behaviors) require the Python threading module to be initialized properly to work across threads.

If the Python threading module isn’t imported early, internal thread management might fail silently.



Recommended Solution

1. Import Python’s threading Module Early

Add a Python threading import right after starting the Python engine in your Unity C# code, before calling BeginAllowThreads():

[[See Video to Reveal this Text or Code Snippet]]

This ensures Python’s threading infrastructure is properly initialized, which many libraries depend on.

2. Careful Semaphore Management

Your use of SemaphoreSlim.WaitAsync() with try/finally is mostly correct, but watch out for exceptions during WaitAsync() calls that could cause semaphore imbalance. Always handle exceptions carefully to avoid deadlocks.

3. Debug and Analyze Threads

Use debugging tools to inspect thread states during asynchronous imports.

Verify no deadlocks or thread contention are occurring.



Additional Tips

Prefer using Task.Run over manual thread management for async loading.

Ensure all Python calls that access the Python runtime use Py.GIL() to acquire the GIL.

Consider lazy-loading heavier Python modules synchronously at startup if the async complexity outweighs UI blocking.



Summary

Loading Python modules asynchronously with pythonnet in Unity requires careful threading and GIL management. Importing the Python threading module early ensures that internal threads in your Python libraries work correctly.

By adopting this approach, you can maintain a responsive Unity UI while safely integrating complex Python modules.