Step Over, Step Into, and Step Out not working when debugging Flask app served locally using gunicorn

[jdwestwood]

Version: 1.96.2 (user setup)
Commit: fabdb6a30b49f79a7aba0f2ad9df9b399473380f
Date: 2024-12-19T10:22:47.216Z
Electron: 32.2.6
ElectronBuildId: 10629634
Chromium: 128.0.6613.186
Node.js: 20.18.1
V8: 12.8.374.38-electron.0
OS: Windows_NT x64 10.0.19045

Running in Win10/WSL2 with Python 3.12.
VSCode Python Debugger v2024.12.0 and later, up though the current pre-release v2024.15.2024121701.

In launch.json, I have the following (simplified) config for debugging my Flask app using gunicorn[gevent] v23.0.0 (the latest version) to serve it locally:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Launch gunicorn",
            "type": "debugpy",
            "request": "launch",
            "python": "/path/to/python/venv/bin/python3.12",
            "program": "/path/to/python/venv/bin/gunicorn",
            "cwd": "${workspaceFolder:flask_app}",
            "gevent": true,
            "args": ["startup:app",
                     "--bind=localhost:8080",
                     "--workers=1",
                     "--worker-class=gevent"],
        },
}

A simplified version of the entry-point file startup.py that reproduces the bug is:

# Set a breakpoint 1 here.
a = 1

# Step Over or Step In to here.
b = 2

# Set breakpoint 2 here.
c = 3

# For the purpose of illustrating the bug, these lines can be commented out.
# from flask import Flask
# app = Flask('Flask_App')

In Python Debugger v2024.10.0, when I launch "Launch gunicorn" everything works as expected: after hitting breakpoint 1, I can "Step Over" or "Step In" to b = 2.

In Python Debugger v2024.12.0 and subsequent releases, execution stops as expected at breakpoint 1, but clicking "Step Over" or "Step In" causes execution to resume until breakpoint 2 is hit.

For the time being as a workaround, I have pinned Python Debugger at v2024.10.0.

[escopeland]

Using Flask's development server instead of gunicorn leads to the same problem. Reverting to Python Debugger v2024.10.0 works.

[v-zubarev]

I have the same issue in regular Python code (debugger running in WSL). Debugger only respects breakpoints, but no step controls.

Reverting to 2024.10.0 helps.

[eleanorjboyd]

Is this happening for a different version of debugpy or just for the debugger extension?

[jdwestwood]

After reading the post from @v-zubarev, I installed Python Debugger v2024.14.0 (latest release). If I run startup.py using the "Python Debugger: Debug Python File" button at the upper right of the editor tab, the step controls work as expected for me. In other words, I am not experiencing the behavior described by @v-zubarev.

Only when I run startup.py via gunicorn as I described in my original post do the step controls not work.

[jeffsawatzky]

I think this breaks "justMyCode=false" as well. I was having issues with stepping into third-party library code while trying to debug a unittest, but as soon as I downgraded to v2024.10.0 it all worked fine.

My launch.json file looks like:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: Debug Tests",
            "type": "debugpy",
            "request": "launch",
            "program": "${file}",
            "purpose": ["debug-test"],
            "console": "integratedTerminal",
            "justMyCode": false,
        }
    ]
}

And with v2024.14.0 I can't step into library code, but with v2024.10.0 I can.

[maor-outrival]

I was having the same issues with debugging a subprocess. Step Over and Into did not work, only Continue. After banging my head against the screen for many days and trying many configs, I confirm that downgrading to v2024.10.0 solved the issue.

Please fix this, it's been 7 months since that version came out.

[v-zubarev]

Yeah I confirm that when I had the same issue back then, it was for subprocesses. Regular scripts/services can be debugged fine.

[ntsphwoelfel]

Just had the same issue and a downgrade to v2024.10.0 worked. Previous version was 2025.10.0.