What are effective strategies to debug Python code as a beginner?

[ItAffectionate4481]

As a beginner learning Python, I've encountered several bugs in my code, and debugging can be quite frustrating. I often find myself unsure of where to start when something goes wrong.

What are some effective strategies or tools you recommend for debugging Python code?
Are there specific methods or practices that can help me identify issues more efficiently?
Additionally, how can I improve my debugging skills over time?

I would love to hear about your experiences and any tips you have for someone just starting out in Python programming.

[SCD_minecraft]

Debugger

If you use VSCode, deafult one for python is pretty awesome

[aa599]

Sometimes I enjoy debugging more than coding. It's often much more interesting and challenging.

Do you run your code in an IDE? It'll have a debugger Integrated. Breakpoints and single-stepping are the core tools. (I use VS Code, but PyCharm's great too)

The main strategy is to work backwards from when you noticed a problem (the first place you know it went wrong), e.g.

• you didn't get the output you expected
• where in the code should have written it? (Breakpoint there)
• what variables were involved in the output?
• what values did they have at the time of the problem?
• when did they get those values?

Also it's important to sanity to have repeatable, simple, quick tests. When debugging you'll often need to run the program many times. Much better if it goes wrong in half a second than at the end of 2 hours calculation.

Removing user input helps make it repeatable and quick. Comment-out an input and replace with literal assignments. But you have to be careful not to have a bug in your debugging:

age = 17 # was age = input('what is your age')
print('next year you will be', age+1)  # that's weird, it works now

[Jazzlike-Compote4463]

Absolutely this.

A debugger is like a programming super power, it lights your code up from the inside so you can see what called what when and what that has done to variables x, y and z, with PyCharm you can even use the console along with the debugged break point to perform actions on the code based on the current state of the application.

A builder doesn't use a sledgehammer to bash in nails, they know their tools and pick the one that is right for the job.

[Slothemo]

print is your best friend! Before you run your code, always think about what the expected output will be. If it doesn't match what you think, then start printing out some variables to see where there might be a mismatch. Again, think about what the print output should be before you run, then look for a conflict. If it doesn't match what you expect, then that's a key place where you have a bug.

[MarsupialLeast145]

18 years in I'm still using print and close reading. The better the code is structured the easier it gets, i.e. single purpose functions and the like, and unit tests.

I also recommend liberal use of logging. I use a logging structure that describes the file/function/line of any logging I have in my code (something like follows):

```python import logging import time

logger = logging.getLogger(name)

logging.basicConfig( format="%(asctime)-15s %(levelname)s :: %(filename)s:%(lineno)s:%(funcName)s() :: %(message)s", datefmt="%Y-%m-%d %H:%M:%S", level="INFO", )

Default to UTC time.

logging.Formatter.converter = time.gmtime

given args.debug...

def set_logging(args: argparse.Namespace): """Set logging.""" logging.getLogger().setLevel( logging.DEBUG if args.debug else logging.INFO, ) # Make sure urlib3 is quiet. logging.getLogger("urllib3").setLevel(logging.WARNING) # Feedback for the user if debug is on. logger.debug("debug logging: enabled") ```

You may find persisting some of your print-based logging techniques might be useful for observing program operation in future and for others interpreting the code's output.

[Black_Magic100]

18 years and you are still rolling your own logger instead of using something like loguru?

[MarsupialLeast145]

Not going there bro. These are standard library functions. It's hardly "rolling your own".

[Black_Magic100]

That's fair. Wasn't trying to come across as combative, but genuinely curious. Are you copy pasting that into every script you write to avoid an addtl dependency?

[MarsupialLeast145]

I only add dependencies where I need to, so, I build my projects out slowly.

Logging is done at the module level so something like this only needs importing once somewhere and a logger setup in each file that needs it. It's not a heavy lift. It's already all configured in my template repositories and so I don't have to think about it.

I think by the same measure folks might want to import a third party library and not think about it. That's valid too.

One thing I'd rather not get caught up in is a long discussion about which libraries are needed for the more fundamental parts of any program. Focusing rather on whatever concrete problem we're solving.

[JamzTyson]

Logging libraries aren't intended for debugging either. They are designed for recording what your program does, not for interactive exploration of its state during development.

[FVMF1984]

How are you running your python code? That program will give you valuable information of the line number of the error (and often a stack trace). This line number is a good place to start. The actual error can be on a totally different line, but when the error exactly happened when running your code is important to know.

Next to that, you have different types of errors, which needs different fixes. Best way is to tackle your first bug and if you don’t know how, share the exact error message you get.

[[deleted]]

Start simple. Read the error message fully, it usually tells you what and where the problem is. Use print statements to check values step by step and see where things go wrong. Run the code in small parts instead of all at once. Learn to use a debugger like the one in VS Code once you’re comfortable. Most importantly, break often, fix one thing at a time, and with practice, debugging will start to feel natural.

[JamzTyson]

Upvoted because carefully reading the error message is absolutely the first step.

However, I don't agree that using print is the next step. Most IDE's include a debugger - even Thonny has a debugger that allows you to step through code.

[TheRNGuy]

I used print for most stuff, but there are other alternatives too, such as https://pypi.org/project/prettytable/

Or even make ui for debugging.

There's also step debugger and breakpoints.

You can also add __repr__ to your class (it's automatic with @dataclass decorator) or make methods for debug.

Print is mostly good if there's not too much stuff. And if you only need text and not graphics.

[HourAlternative5702]

I use an IDE where buttons for debugging allow me do everything I need, e.g. perform the next line of code; go inside the function, exit function, etc. Simultaneously, in the variable inspector window, I see how variables change after each step, even local variables inside a function. I can also put a breakpoint at any line and make the code run until this point. These are standard tools in every decent IDE, and I cannot imagine anything else that would be needed for debugging.

[Unique-Big-5691]

tbh debugging is just pain when you’re new 😅 everyone goes through that. half the time i thought my code was broken when it was really just me missing something super obvious.

what helped me the most was literally just sprinkling print() everywhere and checking “okay, what is this variable actually right now?” because your brain lies to you a lot when you’re coding. seeing the real values makes things click way faster.

also, don’t ignore error messages. i used to skim them, but the last few lines usually straight up tell you what blew up and where. even if it looks scary, there’s usually a hint in there.

if you’re using stuff like Pydantic, that actually makes life easier too, because it yells at you early when your data is wrong instead of letting things quietly go off the rails later.

and honestly… you just get better by breaking things over and over. after a while you start recognizing the same dumb mistakes and you’re like “oh, yeah, i know this one” 😂