Blender Debugger for VS Code (and Visual Studio)

Inspired by Blender-VScode-Debugger which was itself inspired by this remote_debugger for pycharm as explained in this Blender Developer's Blog post.

Since the VS Code one wasn't really well documented and it looked kind of dead, once I figured it out, I was just going to add the documentation, but then I ended up rewriting the whole thing.

Now it can:

• Auto-detect where python is and auto set the path to debugpy if installed.
• Tell you when the debugger has actually attached.

How to Use

I have made a video (click the image below) for those who just started messing with python in Blender or programming in general, but if you're semi-familiar with Python, VS Code, and the command line the following should make sense. If you have any questions or suggestions, don't hesitate to file an issue.

NOTES/EDITS

• This video was done with blender 2.79, but everything still works mostly the same. Only changes are:
  • Blender changed the default shortcut to the search menu.
  • ptvsd has been replaced by debugpy
  • Blender now requires you enable Settings => Interface => Developer Extras before you can see the commands.

Note on Downloading

You must down it with the the green Clone or Download button above. DO NOT download it from releases!

This is because blender has a problem with the periods in the name from the version number. It used to be you could rename the zip, but this no longer works, you'll get an error when you try to enable the addon. The onyl fix is to go where the addon was installed and rename the folder there.

Installing Python and Getting Debugpy

Install Python 3 with pip and check add to PATH.¹

• If you already have python installed and you can run it from the command line (aka PATH is set), the addon should find it. It checks where python or whereis python or which python to try and determine where python is and uses the first path given².
• If you are using something like Conda and want to use a virtual environment, to have the addon auto-detect the path you can: activate the environment, run Blender from the command line, and it should work.

pip install debugpy

• For Visual Studio, the debugpy version that works depends on the Visual Studio version. I have never used Visual Studio, but you can find more info on setting everything up here: Remotely Debugging Python Code on Linux. (it is not Linux specific)

Setting up your Addon

This is the most important part. Otherwise it won't work. I thought it was my VS Code config but no, it was this.

In Blender go to: User Preferences > File and set the path to Scripts to the folder you're developing your addon in (e.g: "C:\Code\Blender Stuff") BUT the folder must look like this:

Blender Stuff
└── addons
    ├── your-addon-folder
        ├── __init__.py
        ├── ...etc
    ├── another-addon
    ├── ...

See [Blender Docs => Installing Add-ons => User-Defined Add-on Path](https://docs.blender.org/manual/en/latest/editors/preferences/addons.html#:~:text=Add%20a%20subdirectory%20under%20my_scripts%20called%20addons%20(it%20must%20have%20this%20name%20for%20Blender%20to%20recognize%20it) for details.

Now remove your addon from Blender if you had installed it manually already, save settings, and when you restart your addon should be installed automatically.

Setting up this Addon

Install the addon.

If it did not find the path it'll say "debugpy not found", you'll have to set it manually. It's wherever python is + "\lib\site-packages". NO trailing backslash.

If you want, increase the timeout for the confirmation. It'll print "Waiting..." in the console every second until it prints it's timedout. This does not mean the server has timedout just the confirmation listener.

If you're using Blender 2.9+ you must turn on Developer Extras (Preferences => Display => Developer Extras) if you haven't already, otherwise the addon's commands won't turn up in the search.

Open up Blender's search (default shortcut: F3), type "Debug".

Click Debug: Start Debug Server for VS Code.

Note: you can only start the server once. You cannot stop it, at least from what I understand. If you run it again it'll just tell you it's already running and start the timer again to check for a confirmation.

Connecting the Editor

Open your addon folder (e.g. "C:\Code\Blender Stuff\addons\myaddon").

Install the Python extension for VS Code if you haven't already. For Visual Studio see Installing Python Support.

In the lower left (see #3 here), VS Code should have auto detected your Python install and set it as the interpreter. For Visual Studio see Managing Python Environments.

Go to the Debugging tab and add a configuration. Pick Python. You'll want the configuration that looks like this, no need to change the defaults, you can delete the rest.

    {
        "name": "Python: Attach",
        "type": "python",
        "request": "attach",
        "port": 5678, //careful, this used to be 3000 in older versions of vscode and this addon
        "host": "localhost"
    },

Now when you run the debugger with this config in Blender and VS Code the console should print "Debugger is Attached" if it was still waiting (it should still attach even if it wasn't, it just won't tell you).

How to Use

At this point you should be able to add a breakpoint and when you trigger it in Blender, Blender should freeze and VS Code should pause on the breakpoint.

Note though that if you make changes to the file, Blender will not detect them. Have open User Preferences > Addons so you can toggle your addon on and off when you make changes. If anyone knows any way to improve this I'd love to know.

Advanced Usage

Wait for Client

The debugger can be made to wait for a client to connect (this will pause all execution). This can be useful for debugging the connection or when running blender headless / in background mode.

To do so, call the server connect command from the python console or from a script/addon like so:

bpy.ops.debug.connect_debugger_vscode(waitForClient=True)

Running in Headless Mode

First make sure the addon is installed, enabled, and works when you run blender normally.

Blender can then be run in background mode with the -b/--background switch (e.g. blender --background, blender --background --python your_script.py).

See Blender Command Line.

You can detect when blender is run in background/headless mode and make the debugger pause and wait for a connection in your script/addon:

if bpy.app.background:
    bpy.ops.debug.connect_debugger_vscode(waitForClient=True)

This will wait for a connection to be made to the debugging server. Once this is established, the script will continue executing and VSCode should pause on breakpoints that have been triggered.

For addons, you will need to do this from a handler:

from bpy.app.handlers import persistent
#...
def register():
   bpy.app.handlers.load_post.append(load_handler)
#...
@persistent
def load_handler(dummy):
    # remove handler so it only runs once
   bpy.app.handlers.load_post.remove(load_handler)
   if bpy.app.background:
      bpy.ops.debug.connect_debugger_vscode(waitForClient=True)

See Application Handlers

Debugging/Editing Source Code

It is possible to edit the Blender source code but it can be a bit tricky to get it to detect changes (nevermind live editing is buggy anyways).

From blender you can right click just about anything and click "Edit Source" to get it in the text editor. Then to find the path of the file, go to Text > Save As and copy it from there.

Open the file in VS Code, connect to the debugging server, make a change and save it.

Now in Blender the text editor will show this little red button in the top left. Click that and reload the file. Then in Text Editor > Properties turn on Live Edit if you haven't already. Now to actually get Blender to detect any changes you made just type a single character (like add a space anywhere) and then it will detect your changes.

Debugging/Editing Scripts

See [Issue #4](https://github.com/AlansCodeLog/blender-debugger-for-vscode/issues/4) for a workaround.
In the future if I have some time, I might see if there's something I can do to make this easier.

Troubleshooting

• Check you installed the correct debugpy version. With VS Code this should no longer be an issue, but I believe different versions of Visual Studio need different versions of debugpy (see Installing Python Support).
• To determine whether the problem is on Blender's side or your editor's: Close Blender and this test script, you can copy/download it or run it from the addon folder. Run it with Python python test.py, and then try to connect to the server with your editor. If you're still getting problems then the problem is with VS Code, try:
  • Check your detected your Python install, or set it manually.
  • For VS Code try reinstalling the VS Code Python extension.
• If you've been using this addon for a while and it's suddenly giving you a connection error, it might be because the default port has changed. VS Code's Python extension (vscode-python) has changed their default port from 3000 to 5678, so I have changed the default accordingly. I've made it configurable now though, so just check the port the addon is set to matches the one in your launch.json in VS Code.

Otherwise, if none of that helped, don't hesitate to file an issue.

Notes

1. Technically, the add-on will work with Python 2 as well since it doesn't use Python itself, just the debupy package, so it doesn't really matter whether you installed it with Python 2 or 3 because the package is compatible with both. On the VS Code side though, the Python extension does need to know where Python is (though not debugpy), but it will still connect if it's using Python 2, but your IntelliSense recommendations will be wrong in VS Code.

2. The addon also detects python if PYTHONPATH is set (because Blender will add it to sys.path) or if you used the Python bundled with Blender to install debugpy (but that's a bit of a pain because it doesn't have pip installed, you would have to install it manually).