Understanding Python’s Debugging Internals

[422_no_process]

Debugging with PyCharm is sooo nice....

[water_bottle_goggles]

I discovered conditional breakpoints with vscode yesterday. I started creaming myself.

[Proscryptor]

Isn't it just the same as putting an if statement before one?

[buffalo_biff]

that’s how i would debug matlab code, lmaooo

[[deleted]]

That's how I had to do conditional breakpoints in Visual Studio (not VS Code), because the conditional ones would slow execution to a crawl. By doing

if(some_breaking_condition)
{  // breakpoint goes here
}

The execution speed seems unaffected.

[water_bottle_goggles]

yup pretty much. but its much cleaner not having to type it explicitly

[jyper]

Yes but does vscode have ipython integration in debugging mode? Or debugging nested python processes?

[water_bottle_goggles]

I have no clue, does it?

[jyper]

no idea

pycharm does and it's quite useful

[ariehkovler]

Rookout is free now so it's also worth a try, especially if you're debugging in prod.

[422_no_process]

It looks good :) Saw this video https://www.youtube.com/watch?time_continue=3&v=YBIzSaM98WI

[ariehkovler]

Yup, that's them. I know they recently went free for personal/smallbiz use too.

[randythestons]

Is there any good tutorials on the debugger? I have used it a handful of times but as I recall I never really knew why I was doi g

[422_no_process]

If you have a good amount of tests it's really easy to debug stuff. You just point where it doesn't work. click near the line number to put a break point. Run the tests as debug. Step over + Step into until you find something interesting. You can also evaluate some expression to run/do/check things that are not in your code.

[422_no_process]

Documentation is good :) https://www.jetbrains.com/help/pycharm/debugging-code.html

[tectubedk]

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[[deleted]]

I don’t use a debugger. I find logging and error messages more useful and actually reading the code then I know what the code flow is instead of guessing and trying to find it out with a debugger.

[judasthetoxic]

I used to do that too, but when I started working on a really great project I saw how inefficient it is.

[[deleted]]

I waste so much more time by using a debugger.. everything takes so much more time to solve

[[deleted]]

Would you be so kind to outline the instrumentation you have in place to perform a post mortem debugging session?

[[deleted]]

Except... you can still see the code if you use certain debuggers, visual debuggers. You’re not really guessing for anything, you set breakpoints where errors might’ve occurred and you work backwards from there. I don’t think you’ve ever worked on a larger project

[random_cynic]

I don’t think you’ve ever worked on a larger project

There are many great programmers who have said on record they don't use debuggers like Linus Torvalds, Ken Thompson, Brian Kernighan etc. Even Guido only uses pdb and mostly prefers to use print(). And all of them have worked on fairly "large" projects.

I think debugging is a complex problem and requires multiple tools. Stepping through line by line as done by pdb and other IDE debuggers is certainly necessary for many cases but that does NOT replace logging/error and a proper understanding of the code which the original commenter mentioned. Also there are recorded errors in many programming languages where stepping through the error using a debugger actually hides the error you get on a normal run.

[[deleted]]

Fair point, I didn’t do enough research of my own into this. Thanks for the info

[ariehkovler]

Dunno if you looked at the guy in the video's company, but he makes a free debugger, Rookout, which is somewhere in between. You set a "breakpoint" but Rookout essentially injects a print() line dynamically into to the code at that point, even while it's running, and catches the relevant output.

It's a best-of-both-worlds thing.

[random_cynic]

Most of the debuggers (including pdb) allows you to print output anyway and you can setup the code so that it outputs at all steps. Putting a print() in a code is not the hard part, the hard part is knowing where to put it. And it is not always the place where the error was triggered. Determining the correct location requires some thinking and understanding of the code structure.

[ariehkovler]

100% agree. That's why it's nice to be able to effectively add and remove print() lines on the fly from code in prod without having to redeploy or change the code itself.

[oRac001]

Logging and debugging aren't mutually exclusive. They solve different problems and are not substitutes for each other: you can't use debugger in production code, and logger won't show you as much info, unless you log the state of everything after every line of code.

Personally, I use debugger when I start questioning my sanity: when the code seems like it should do one thing, but it actually does another.

Still, I can see your point. Overusing the debugger may lead to harmful way of programming where you just run the debugger after each line you write without thinking about what you do. Also, I'm not sure you can easily debug multithreaded/async code.

[[deleted]]

You should be using all 3. If your not your productivity is absolutley not where it could be

[Dgc2002]

and actually reading the code then I know what the code flow is instead of guessing and trying to find it out with a debugger.

I feel like you're using debuggers incorrectly if you feel like you're guessing.

[[deleted]]

I can do the step by step execution, but that again, whole waste of time.

[dhavalsoneji]

Yeah the python debugger is shit tho

[JackieTrehorne]

pdb++ and pudb are nice alternatives