RuntimeError: `launch_passive` requires that the Python script be run under `mjpython` on macOS

The error message you're seeing, RuntimeError: launch_passive requires that the Python script be run under mjpython on macOS, suggests that you are trying to execute a Python script that interacts with or requires the MuJoCo physics engine, specifically in a passive way (without an active simulation window, perhaps for batch processing or background computations). This operation requires the use of a specialized Python interpreter provided by MuJoCo, known as mjpython, when running on a macOS system.

Here's how to address this issue:

1. Ensure MuJoCo is Correctly Installed

First, ensure that MuJoCo is correctly installed on your macOS. Follow the installation instructions provided by MuJoCo. This often involves downloading the MuJoCo binaries and placing them in a specific directory, and setting environment variables such as MUJOCO_PY_MJKEY_PATH and MUJOCO_PY_MUJOCO_PATH to point to your MuJoCo license key and the MuJoCo installation directory, respectively.

2. Using mjpython

• Locate mjpython: Once MuJoCo is installed, locate mjpython within your MuJoCo installation directory. It's a Python executable specifically tailored for MuJoCo applications.
• Run Your Script with mjpython: Instead of running your script with the standard python command, use ./mjpython script_name.py (assuming you are in the directory containing mjpython, or you've added its location to your PATH environment variable). Replace script_name.py with the path to your Python script.

3. Adjusting the Environment (if necessary)

If you're running scripts from an IDE or need to integrate with an existing Python environment, you might need to adjust the environment to recognize mjpython. This can involve:

• Setting PATH: Ensure the directory containing mjpython is in your PATH.
• Virtual Environment: If you're using a virtual environment, you might need to create a symbolic link within the environment's bin directory to point to mjpython, or adjust the environment's settings to recognize mjpython as the Python interpreter.

4. Additional Considerations

• Compatibility: Ensure your code and other dependencies are compatible with the version of Python used by mjpython. It might differ from the system's default Python interpreter.
• Environment Variables: Some scripts require environment variables specific to MuJoCo or the project you're working on. Ensure these are correctly set in your shell or IDE.

5. Troubleshooting

If issues persist:

• Check Dependencies: Make sure all required libraries and dependencies are installed and accessible to mjpython.
• Consult Documentation: MuJoCo and any related libraries (e.g., mujoco-py) often have detailed documentation and troubleshooting guides.
• Community and Support: Look for help within the MuJoCo community forums or places like Stack Overflow. Provide detailed information about your setup and the issue you're encountering.

Following these steps should help you resolve the launch_passive error and effectively run your script under mjpython on macOS.