VSCode python debugger incredibly slow / unresponsive / slow repr / spinning icons in "Variables" pane

[apmoore499]

Debugging python scripts has become very slow in the last few days, I don't know why. Rolling vscode back to previous version didn't fix anything. The performance is very laggy whereas previously it worked very fast.

Steps to reproduce:

1. Run debug with basic config:
   {
   "name": "Python: Current File",
   "type": "python",
   "request": "launch",
   "program": "${file}",
   "console": "integratedTerminal",
   "justMyCode": true,
   "logToFile": true
   },
2. Click on arrow to start debug

The following issues are encountered:

• Breakpoints take ages to hit. However, the script contents are simple and should not take this long, so it seems the problem is with debugger.
• Messages indicating slow repr computation: "pydevd warning: Computing repr of da (ConfigDict) was slow (took 141.01s) ". I have never seen this message before. The script I am debugging runs fine if I call 'python script_name.py' without debug. ConfigDict object is from ml_collections package. I have used this package for months without any issues.
• After code has hit a breakpoint, if I try to query any variables by calling 'print(variable_name)' to the debug console, it prints no output. The cursor is still blinking. If I leave it for a few minutes, it might print the variable. It doesn't appear to be completely frozen, just going very slow.
• In debug panel on right hand side, under the 'Variables' section, there are only two displayed items: locals, and globals. These two items are accompanied by a spinning icon that never stops, even when a breakpoint is hit. Additionally, there are no variables listed underneath if I try to click the dropdown arrow. Again, if I leave it for a few minutes, a list of variables may populate eventually.

I have attached debug.log files.
debugpy.adapter-7080.log
debugpy.launcher-6365.log
debugpy.launcher-7104.log
debugpy.pydevd.6370.log
debugpy.server-6370.log

debugpy.adapter-6340.log

[apmoore499]

Issue has been fixed.

The issue was caused by an instance of ml_collections ConfigDict() class. A neural net was added to the dict which caused the slowdown. The network has ~22million weights. I believe this causes slowdown in repr as vscode debugger may be running repr query for all parameters in network. Have not confirmed if this is the exact cause, regardless I have changed code and no slowdown.

Example of code which throws the issue:

import ml_collections
cdict=ml_collections.ConfigDict()
neural_net=load_my_neural_net()
cdict.neural_net=neural_net```

[int19h]

To clarify, debugger uses repr() to compute the representation of variables that it needs to show in Variables, Watch etc. If you have a breakpoint, this happens every time that breakpoint is hit.

[poedator]

in my case this did not help.
Somehow debugger continues trying to calculate repr for heavy variables, even though the variables panel was switched off...
There was noting in the watches either.

[rchiodo]

That would depend upon VS code (or Visual Studio) or whatever your IDE is sending a variables request. If you turn on logging, the vscode log should show if there is a variables request or not.

[dbolser]

Can this be turned off? Generally I don't look at 'variables' and just stick to the debug console

[rchiodo]

Not sure if this prevents the request from being made but you can hide the variables pane:

[DylanSp]

I ran into this issue when working on a project involving Z3's Python bindings. Hiding the variables pane did not prevent the request being made; what worked was overriding __repr__ for a dataclass in my code that contained Z3 objects.

Thanks for the pointers on what to look at - I'm posting this for the benefit of people searching in the future.

[kaikai23]

Not sure if this prevents the request from being made but you can hide the variables pane:

This works for me, thanks!