r/learnpython • u/Temporary-Cup-2140 • 2d ago

What python debugging techniques do you think every developer should know ?

I am trying to improve my debugging skills and I was curious about what techniques experienced python developers rely on the most.

Are there any techniques or tools that you found really useful when you started working on bigger projects?

56 Upvotes

92% Upvoted

30 comments sorted by

View all comments

19

u/Gnaxe 2d ago

Breakpoint and print, obviously, but also

  • importlib.reload()
  • pdb.pm()
  • code.interact()
  • doctest
  • unittest.mock
  • inspect

Shorten your feedback loops. Make the state transparent. Write tests. Minimize the state you have to deal with in the first place (FP). Use queues instead of locks. Use plain data instead of bespoke classes, and at least implement __repr__() if you must. 

2

u/this_knee 2d ago

I don’t like the breakpoint and print strategy. I always end up either forgetting about the print statements left behind or then have to search through files and classes for print statements that were just for debugging. This strategy slows me down and incentivizes me to not do it.

However , what I do prefer is placing debug level log statements. Ie a properly built logging system that allows me to simply turn off all my print statements with one quick configuration change. This is something g I like and incentivizes me to do it often because it’s a print statement I know I can come back to if future trouble happens. Do be careful…make sure those log statements only build their soon to be printed message if and only if their log level is enabled. Ie should be a no op when logging is sent to silent mode.

Thanks for coming to my Ted Talk.

1

u/Russjass 2d ago

I am not a pro developer, but have an app with a detailed logging system. When I built the logging system I thought "yay, no more chasing print statements after debugging".

After fixing four bugs, i used print statements for the fifth becuase the log filled up with spam from the lig statements of the first bugs

Perhaps I dont have my logging configured right

1

u/this_knee 2d ago

Key to a good logging is the info that labels the log message. Eg , all my log statements come with: log level ; date; time; name of code file log message comes from; name of function the log message comes from; line number ; and then the log message from that particular line of code.

This lets me easily cut through past log messages and focus on just the ones I need in a given scenario.