Issue with debugpy affecting objects refcount

[Andrej730]

Environment data

• debugpy version: 1.8.1
• OS and version: Windows 11
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.11
• Using VS Code or Visual Studio: VS Code 1.93.1

Actual behavior

Consider snippet below - when executing with a debugger attached it fails with an error below.

    x.resize(4)
ValueError: cannot resize an array that references or is referenced
by another array in this way.
Use the np.resize function or refcheck=False

import numpy as np
import sys

# import debugpy
# debugpy.listen(5678)
# debugpy.wait_for_client()

x = np.ones(3)
print(sys.getrefcount(x))
# ValueError: cannot resize an array that references or is referenced
# by another array in this way.
# Use the np.resize function or refcheck=False
x.resize(4)
print(x)

Investigating I've noticed 3 different behaviours:

1. Running it just using python test.py - prints 2 as the refcount and produce no errors.

2. Running it using VS Code's "Debug Python File"
   
   or by uncommenting debugpy part and attaching debugger later - it prints 2 but fails with an error.

3. Running it with VS Code/debugpy debugger but setting breakpoint at x = np.ones(3) and then stepping through all lines - then it prints 3 and also fails with an error.

Expected behavior

Code execution not to be affected by the debugging process.

Related - IfcOpenShell/IfcOpenShell#6256

[rchiodo]

I can't reproduce this problem myself on 3.13 or 3.12, so it seems it's only an issue with 3.11 or earlier. I don't think we'd spend time trying to figure out why it doesn't work on 3.11.

[Andrej730]

@rchiodo

Okay, I've installed Python 3.12.7 with debugpy 1.8.13 and got the same issue.

I've executed the same script below with py -3.12 test.py, connected to debugpy using VS Code, set breakpoint on x = np.ones(3) and stepped through all program lines one by one using "Step Over", it printed 3 as the refcount and broke with ValueError: cannot resize an array that references or is referenced on resizing.

Though something indeed is different in Python 3.12 because running script with a debugger attached from VS Code or attaching debugger to already running script prints 2 and doesn't fail.

import numpy as np
import sys

import debugpy
debugpy.listen(5678)
debugpy.wait_for_client()

x = np.ones(3)
print(sys.getrefcount(x))
# ValueError: cannot resize an array that references or is referenced
# by another array in this way.
# Use the np.resize function or refcheck=False
x.resize(4)
print(x)

[rchiodo]

I'm still not reproducing on 3.12. Maybe it's my numpy version.

Doesn't seem to matter. Numpy 1.26 and 2.2.3 didn't have a problem with your code above.

[Andrej730]

Was using numpy 2.0.0, updated it to 2.2.3 and I still get the issue.
Are you sure you're stepping through the code and not just running it? (just running doesn't seem to trigger the issue in Python 3.12, though it does in Python 3.11)
What refcount does it prints for you?

[rchiodo]

Here's the output of the app as I step:

At breakpoint:
(.venv312) PS C:\Users\rchiodo\source\testing\test_pylance> python .\test_debugrefcount.py
2

After breakpoint and step out:
(.venv312) PS C:\Users\rchiodo\source\testing\test_pylance> python .\test_debugrefcount.py
2
[1. 1. 1. 0.]

[Andrej730]

I think I've found one more detail about the issue - it seems having not available variable in "Watch" increases refcount leading to this issue. See the demo below:

1. Empty Watch - no issues
2. xx (not existing variable) in Watch - refcount 3 (and rarily 4 / 2 for some reason), error on resize
3. x (existing variable) in Watch - refcount 2, no issues

(Sorry, had to pack demo into a zip archive as github wasn't allowing to upload it as mp4)
demo.zip

[rchiodo]

Thanks that makes it repro for me.