Pyhon debugger stops at removed breakpoint

[paul-rogers]

Type: Bug

The Python debugger in the VS Code Juypter extension does not recognize when the last breakpoint in a notebook is removed. To see this, create a new notebook and choose a Python kernel. Create two cells:

Cell 1:

def fib(n):
    if n < 2:
        return n
    return fib(n-1) + fib(n-2)

Cell 2:

fib(5)

• Set a breakpoint at the if statement in fib(.).
• From cell 2, choose Debug Cell. The debugger will stop at your breakpoint.
• Remove the breakpoint and click Continue (or press F5, if that is your binding.)
• The debugger will again stop at your now-deleted breakpoint. It will do this each time you click Continue.
• Once execution completes, again choose Debug Cell in cell 2. This time, the debugger runs without stopping at the phantom breakpoint.

It seems the debugger cannot handle the situation in which we go from one to zero breakpoints. Modify the function above to:

def fib(n):
    if n < 0:
        raise Exception("Invalid input")
    if n < 2:
        return n
    return fib(n-1) + fib(n-2)

• Set a breakpoint on the if n < 2 line as above.
• Choose Debug Cell on the second cell. The debugger stops as before.
• This time, remove the breakpoint, and add a new one on the raise line.
• Click Continue (or hit F5). The debugger happily runs the rest of the code without stopping.

This is not a new bug: it has been happening for many months on multiple versions of VS Code, extensions and Python.

Extension version: 2024.11.0
VS Code version: Code 1.96.4 (cd4ee3b1c348a13bafd8f9ad8060705f6d4b9cba, 2025-01-16T00:16:19.038Z)
OS version: Linux x64 6.8.0-51-generic
Modes:

System Info

Item	Value
CPUs	AMD Ryzen 7 9700X 8-Core Processor (16 x 5540)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: disabled_software vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: disabled_off webnn: disabled_off
Load (avg)	1, 1, 1
Memory (System)	60.44GB (35.46GB free)
Process Argv	--crash-reporter-id 5e232e7b-355a-468c-ac4a-02c300f898bd
Screen Reader	no
VM	0%
DESKTOP_SESSION	cinnamon
XDG_CURRENT_DESKTOP	X-Cinnamon
XDG_SESSION_DESKTOP	cinnamon
XDG_SESSION_TYPE	x11

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[eleanorjboyd]

Found this behavior when I tested:

Set a breakpoint at the if statement in fib(.).
From cell 2, choose Debug Cell. The debugger will stop at your breakpoint.
Remove the breakpoint and click Continue
The debugger will again stop at your now-deleted breakpoint. It will do this each time you click Continue.

[paul-rogers]

@eleanorjboyd, thanks for the repro! Good to know it is not just some quirk of my setup.

I just repeated the steps from the description. The behavior still occurs in the latest VS Code and extensions.

Version: 1.97.2 Commit: e54c774e0add60467559eb0d1e229c6452cf8447 Date: 2025-02-12T23:20:35.343Z Electron: 32.2.7 ElectronBuildId: 10982180 Chromium: 128.0.6613.186 Node.js: 20.18.1 V8: 12.8.374.38-electron.0 OS: Linux x64 6.8.0-53-generic

Jupyter extension version: 2025.1.0 (2025-02-07, 02:08:52)

OS is Linux Mint, latest version. updated since the initial bug report: now runs on Wayland rather than X.