Python exception formatting

[mole99]

Hi Matthias!

I often use KLayout together with Python (which is a great combination!), but one point that could be improved are the error messages. KLayout prints the error message, but not where it comes from.

I haven't yet been able to figure out in the codebase where the exceptions are being printed. I assume you use a try/except each time you call user code to catch all exceptions and print them as follows:

try:
    1/0
except Exception as e:
    print(e)

Is this correct?

If you use the traceback module, you can print the exception in the same format as the default handler does:

import traceback

try:
    1/0
except Exception:
    traceback.print_exc()

Maybe this could be used in KLayout?

Leo

[klayoutmatthias]

Hi @mole99,

do you have an example?

I am basically doing the traceback thing (in C++), but exceptions that are carried through the C++ level may loose the original location for example.

Plain Python should work. Like here:

In the debugger:

As message:

This is Ubuntu 22. I hope it's not a platform thing.

Matthias

[mole99]

Hi Matthias,
thanks for your reply!

My use case is when I run pymacros in KLayout without a debugger.

For a 1/0 I get the following output in the terminal:

ERROR: ZeroDivisionError: division by zero
   (class ZeroDivisionError)

There is no reference to the location or module, so it's hard to figure out where the exception occurred.

When I run this in my system Python interpreter, however, I get:

Traceback (most recent call last):
  File "/path/to/file.py", line 1, in <module>
    1/0
    ~^~
ZeroDivisionError: division by zero

Not only the exception is printed, but also its location and module.

Interestingly, different types of errors such as IndentationError print the file and line number in KLayout:

ERROR: IndentationError: expected an indented block after function definition on line 3 (SKY130.lym, line 5) (class IndentationError)

That's probably because it is not an exception and handled differently.

But even then it would be nice if the formatting was the same as in the standard Python interpreter :)

Leo

[klayoutmatthias]

Hmm ... that has to be some special case. Maybe in some places, the trace isn't printed.

I see stack traces all over. For example on Ubuntu with the upcoming 0.29.3 version, but it is the same with 0.29.2 on Windows. I am using this Macro:

I run outside debugger, by showing this macro in menu:

In this case I can close the debugger and run the macro through "Macros/name of macro.lym". In that case, I see a popup

When I click on "Details" I get the stack trace:

On the console, it prints the stack trace too:

And for Windows users, there is the log viewer from "File/Log Viewer" and it also shows the stack trace:

I assume you refer to a specific use case - for example when coding PCells. Also, Qt slots or event handlers may behave differently. But plain Python scripts should show the stack trace.

Matthias

[mole99]

Hi Matthias, yes this is exactly my use case ^^ I would like to get Taher's PCells working, but there are some issues with them.

For me it is enough to add a pymacro like so to reproduce the issue:

<?xml version="1.0" encoding="utf-8"?>
<klayout-macro>
 <description/>
 <version/>
 <category>pymacros</category>
 <prolog/>
 <epilog/>
 <doc/>
 <autorun>true</autorun>
 <autorun-early>true</autorun-early>
 <shortcut/>
 <show-in-menu>true</show-in-menu>
 <group-name/>
 <menu-path/>
 <interpreter>python</interpreter>
 <dsl-interpreter-name/>
 <text>

1/0

 </text>
</klayout-macro>

When KLayout is started from a terminal, I get the error but no trace.

But there is some strange behavior: When the code above is run, then the error is printed 3 times in the terminal on startup:

ERROR: ZeroDivisionError: division by zero
   (class ZeroDivisionError)
ERROR: ZeroDivisionError: division by zero
   (class ZeroDivisionError)
ERROR: ZeroDivisionError: division by zero
   (class ZeroDivisionError)

Also, the log viewer is empty. (Maybe autorun-early is too early for the log viewer.)

If I disable autorun-early, then it is only printed once in the terminal on startup:

ERROR: ZeroDivisionError: division by zero
   (class ZeroDivisionError)

And the log viewer shows the error, but no trace:

If I run the macro manually from the GUI, I get:

Again, no stack trace. Any ideas what I could try?

Btw. I am on Debian trixie and compiled master (0.29.2). The Debian package and the flatpak package also behave the same.

Leo

[klayoutmatthias]

Thanks for trying this - I can confirm I get the stack traces as expected on Ubuntu.

I think there is a Python version dependency. What is the Python version you are using? The default one from Debian trixie?

Thanks,

Matthias

[klayoutmatthias]

When I pull the Debian:trixie docker image and install "python3", I get 3.11.9. Is that your version too?

Thanks,

Matthias

[mole99]

Hi, yes I can confirm that is my version too!

Python 3.11.9 (main, Apr 10 2024, 13:16:36) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

[klayoutmatthias]

Let me try if I can reproduce the problem with the Debian:trixie/3.11.9 combination.

Matthias

[mole99]

On Debian bookworm with Python 3.11.2 I get the same behavior (using flatpak):

[klayoutmatthias]

Reproduces immediately on Debian, not on Ubuntu :(

At least I can debug the issue now.

Thanks,

Matthias

[mole99]

That's good to hear! (At least I haven't gone mad ^^)
If I can help you in any way, please say so.
Perhaps you could point me to the place in the code where the exceptions are printed, so I can see if I can make the formatting similar to Python's stacktrace once the issue is fixed.

Thanks!

Leo

[klayoutmatthias]

I found the issue.

Since Python 3.11.7 the semantics of PyTracebackObject has changed slightly. There is no public API unfortunately, so integrators have to sync with Python development :(

But that is easy to fix.

Thanks for reporting the problem.

Matthias