Error Installing on Arch Linux: "Cannot activate mitsuba-blender add-on. Python pip module cannot be initialized."

[Zi7ar21]

Bug Description

After downloading the latest version of "mitsuba-blender.zip" and attempting to install it, an error pops up:

Cannot activate mitsuba-blender add-on. Python pip module cannot be initialized.

And the add-on is not enabled.

To Reproduce

Steps to reproduce the behavior:

1. Download the latest copy of mitsuba-blender.zip from the releases tab
2. Open Blender (I'm using 4.3.2, but this error should occur on any recent version of Blender)
3. Open Blender's Preferences (CTRL+[,] or Edit > Preferences)
4. Click Add-ons > Add-ons Settings drop-down > Install from Disk...
5. Navigate and select mitsuba-blender.zip
6. Attempt to enable "Mitsuba-Blender" add-on

Expected behavior

The Mitsuba Blender add-on to be enabled without any errors.

Resources

If applicable, add screenshots or other files (Blender projects, Mitsuba scenes) to help explain or demonstrate your problem.

Environment (please complete the following information):

• uname -a output:

  Linux jacobarch 6.12.8-zen1-1-zen #1 ZEN SMP PREEMPT_DYNAMIC Thu, 02 Jan 2025 22:52:21 +0000 x86_64 GNU/Linux
  

• Blender Version: 4.3.2
• Add-on Version: latest

Additional context

Unlike other Linux distros (e.g. Debian), Arch Linux follows PEP 668. This means you cannot simply install packages using pip, the regular way to do it is by first initializing a venv with:

python -m venv [ENV_DIR]

and then using pip from the virtual environment:

[ENV_DIR]/bin/python -m pip install [Package Name]

To understand why this is, see PEP 668, or additionally the thread "What's the story on pip's externally-managed-environment error?" on the Arch Linux forums.

[Zi7ar21]

For reference, here is what happens when I try to install numpy using pip:

[jacob@jacobarch ~]$ pip install numpy
error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try 'pacman -S
    python-xyz', where xyz is the package you are trying to
    install.
    
    If you wish to install a non-Arch-packaged Python package,
    create a virtual environment using 'python -m venv path/to/venv'.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip.
    
    If you wish to install a non-Arch packaged Python application,
    it may be easiest to use 'pipx install xyz', which will manage a
    virtual environment for you. Make sure you have python-pipx
    installed via pacman.

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.

The canonical way of installing numpy system-wide is to use pacman (or your distro's equivalent):

sudo pacman -S python-numpy

I don't know why this error exists with Blender though, I thought it maintained a separate Python installation? Maybe only on Windows...

[AnsonSavage]

IDK if this would fix it, but this helped that error for me.

Did you run Blender with:

<path_to_blender> --python-use-system-env

?

[Wouter-Lemoine]

I'm on Linux wimec 6.12.16-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.16-1 (2025-02-22) x86_64 GNU/Linux and I'm having the same issue:

Exception in module register(): /home/wimec/.config/blender/4.3/scripts/addons/mitsuba-blender/__init__.py
Traceback (most recent call last):
  File "/usr/share/blender/scripts/modules/addon_utils.py", line 511, in enable
    mod.register()
    ~~~~~~~~~~~~^^
  File "/home/wimec/.config/blender/4.3/scripts/addons/mitsuba-blender/__init__.py", line 298, in register
    raise RuntimeError('Cannot activate mitsuba-blender add-on. Python pip module cannot be initialized.')
RuntimeError: Cannot activate mitsuba-blender add-on. Python pip module cannot be initialized.

This happens both with the --python-use-system-env flag and without.

[gianniskokkinis]

I'm fixing this issue by doing these steps. First I find the pip.conf by using this command on terminal:

Run the following command in the terminal to check if a pip.conf file exists:

python3 -m pip config debug

Look for an output similar to:

/etc/pip.conf, exists: False

Modify the file by using this command

sudo nano /etc/pip.conf

and add the following lines

[global]
break-system-packages = true

Install Mitsuba

pip install mitsuba

Modify the Mitsuba-Blender Add-on on this path <</home//.config/blender/4.0/scripts/addons/mitsuba-blender/__ init __.py>>

Comment out the following lines

if not ensure_pip():
     print("something")
     raise RuntimeError('Cannot activate mitsuba-blender add-on. Python pip module cannot be initialized.')

This method works for me.

[merlinND]

Hello @gianniskokkinis,

Thanks for sharing your solution; however not that it is not recommended to enable break-system-packages. Installing packages at the system level (global) may result in upgrading or modifying packages that are used by your OS, rendering it unusable.

[zishenliu729]

I encountered the same problem in the windows environment. But the problem was solved after installing Microsoft Visual C++ Redistributable for Visual Studio 2017.

[cleversonahum]

A workaround is to use Blender from Flatpak instead of installing it directly on your OS. This way, you would use Python from the flatpak container and would be able to install the Mitsuba Blender plugin.