Debugging QGIS 3.x python plugins on OSX using VS Code

notes.md

Debugging QGIS 3.x python plugins on OSX using VS Code

Plugin

In QGIS install the plugin debugvs.

Python dependencies

The debugvs plugin needs the python module ptvsd to function. This module is not installed by default.

In principle you just pip install ptvsd in the python interpreter used by QGIS.

I am using the QGIS OSX installer from Lutra Consulting. This installer works really great, but installing additional python modules is not very easy.

What I did was this:

1. Download the ptvsd wheel from pypi. I tried with the newest version (4.2.4), but that didnt work for me. I ended up using ptvsd-4.1.4.zip.
2. Unzip the wheel (if it has the extension .whl then rename it to .zip)
3. Inside the zip there are two directories. Copy the directory ptvsd to the Resources/python of your QGIS installation. In my case this was /Applications/QGIS3.6.app/Contents/Resources/python/.

Restart QGIS.

Setting up VSCode

The default remote debugger configuration in VS Code looks like this

{
    "name": "Python: Remote Attach",
    "type": "python",
    "request": "attach",
    "port": 5678,
    "host": "localhost",
    "pathMappings": [
        {
            "localRoot": "${workspaceFolder}",
            "remoteRoot": "."
        }
    ]
},

I had to change the pathMappings to get it to work:

{
    "name": "Python: Remote Attach",
    "type": "python",
    "request": "attach",
    "port": 5678,
    "host": "localhost",
    "pathMappings": [
        {
            "localRoot": "${workspaceFolder}",
            "remoteRoot": "${workspaceFolder}"
        }
    ]
},

Debugging

• In QGIS click Plugins -> Enable Debug for Visual Studio -> Enable Debug for Visual Studio
• You should now see a message in the QGIS message bar saying something like DebugVS : Run the Debug in Visual Studio(Python:Attach)
• In VS Code start debugging using the Python: Remote Attach configuration defined above.

Now you should be able to set breakpoints in VS Code.

Hi, from another post I realized that I needed to specify the python interpreter path in debugpy.configure() thus following this thread,

debugpy.configure(python=r"path_to_qgis_python_")
debugpy.listen(...)

I am now able to launch the server and connect via VS Code. Thank you!

@rhinejoel
Thanks for the useful information!
Above path_to_qgis_python_ part was important in my case (using official download version (qgis-mac-ltr.dmg)), because specifying only python3 uses another system python (/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/Resources/Python.app/Contents/Python).
The following works on my environment.

@@ -48,6 +48,8 @@
             import debugpy
 
             self.debugpy = debugpy
+            self.debugpy.configure(python=r"/Applications/QGIS.app/Contents/MacOS/bin/python3")
+            self.debugpy.listen(...)
         except:
             pass
         self.port = 5678