Changing the stack format of pdb

Core Development
1

Hi all,

There’s an issue Improve stack trace from where command in pdb · Issue #104316 · python/cpython · GitHub proposing an improvement for pdb stack output. The format not only lives in “where” command, but also every time the debugger is triggered.

I like the proposal, but it’s a breaking change and might affect the existing tools that depend on it.

The reason I like it is because it displays the most interesting information at the start of the line - where most people pay attention to first. Also, it would be nice to have a consistent file:lineno format in pdb(breakpoint uses it).

Before

(Pdb) w
  /home/gaogaotiantian/programs/cpython/scrabble.py(5)<module>()
-> f()
> /home/gaogaotiantian/programs/cpython/scrabble.py(3)f()
-> a = 1

After

(Pdb) w
  <module> (/home/gaogaotiantian/programs/cpython/scrabble.py:5)
-> f()
> f (/home/gaogaotiantian/programs/cpython/scrabble.py:3)
-> a = 1

Anyone has opinions on this change or something that I did not think of that could negatively affect the users?

1 Like
2

Don’t want to enter a bikeshed argument, but the current format with the function name at the end is consistent with regular exception tracebacks.

3

That’s true, but in tracebacks, it’s much better formatted and the function name stands out well.

File "/home/gaogaotiantian/programs/cpython/scrabble.py", line 3, in f

is significantly better than

/home/gaogaotiantian/programs/cpython/scrabble.py(3)f()
4

Then why not make pdb tracebacks more similar to exception tracebacks?

5

Hi!

I think this is “little” change with a big impact. I’m not sure, but it can break not only tests, also other tools (I don’t know). Did you check those points?

6

That’s another possibility. My concern is that if the stack format is too similar to the exception, the user might think they got an error when they print the stack - it’s just their impression when they see that format.

7

Yes, we need to change tests for pdb, and it’s possible that other libraries rely on that format, and that’s why I’m asking for opinions. The test modification for pdb is easy, I don’t know how many tools out there are relying on this specific format. pdb is a relatively independent tool and I believe most of the debuggers that are built on pdb are implementing the stack format themselves.

It is definitely a trade off. I’m in favor of changing it but I’m not pushing it. I’m open to all ideas and suggestions.