"List index error out of range" when debugger breaks on uncaught exception

[kunom]

Environment data

• debugpy version: 1.8.7
• OS and version: Windows 11
• Python version (& distribution if applicable, e.g. Anaconda): 3.13.0, downloaded from python.org
• Using VS Code or Visual Studio: VS Code

Actual behavior

When the debugger breaks on an exception, the following output appears in the terminal:

2.79s - Error on build_exception_info_response.
Traceback (most recent call last):
  File "c:\Users\mek\.vscode\extensions\ms-python.debugpy-2024.12.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py", line 1533, in build_exception_info_response 
    stack_str = "".join(stack_summary.format())
                        ~~~~~~~~~~~~~~~~~~~~^^
  File "c:\Program Files\Python313\Lib\traceback.py", line 749, in format
    formatted_frame = self.format_frame_summary(frame_summary, colorize=colorize)
  File "c:\Program Files\Python313\Lib\traceback.py", line 553, in format_frame_summary
    last_line = all_lines_original[frame_summary.end_lineno - frame_summary.lineno]
                ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
IndexError: list index out of range

Expected behavior

The output distracts. Also, there might be functional degradation.

Steps to reproduce:

In Visual Studio Code, enable "halt on exception", F5-debug a file that throws an exception

[rchiodo]

That error looks like a bug in Python itself, not the debugger. The traceback module shouldn't throw an exception when asking for a format.

[rchiodo]

I can't reproduce the issue either.

This is the code I used to reproduce:

i = 0
while True:
    x = 1 / i # Exception thrown here

No output in debug console for me:

[rchiodo]

Maybe the exception you're throwing has something to do with the issue. Can you provide a code sample?

[kunom]

Minimal reproduction see below. The issue is triggered by having the parameters to the query call distributed over multiple lines.

def query(url, params=None, json=True):
    raise Exception("foo")

query(
    "",
    params=None,
    json=False,  # distribute your parameters over multiple lines!
)

Results in:

---

By the way, but maybe not related, if you select "break on raised exception", it tries to load a packed variant of the standard library, which does not exist:

[rchiodo]

The raised exception error is expected when you have 'justMyCode' set to false. That's an internal error that is always thrown when running.

[rchiodo]

Thanks, I can reproduce the issue with your query exception. It looks like a bug here:

debugpy/src/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_comm.py

Line 1527 in f4ba976

if line_col_info is not None:

That code needs to make sure the line numbers are not none before adding it to the summary.

[rchiodo]

Actually, it was slightly more complicated. Not sure how this worked in 3.11 and 3.12 but the frame summaries we were generating didn't have the correct line text.

[bartvanandel]

Thanks for this fix! Just yesterday I ran into this as well when debugging some python code suffering from a circular import chain. I just monkey-patched the installed ms-python.debugpy extension with this fix, and it resolved the issue (after cleaning any __pycache__ dirs and restarting the extension host). I'm hoping for a quick release of that extension, thanks! 🚀