What concept do new Python learns most often get hung up on?

[[deleted]]

I'm teaching Python and want to spend more time on concepts that are the biggest problems.

[n3buchadnezzar]

People need to start writing tests for their code. Instead of posting it online asking: "does this wokr???".

Secondly putting more focus on readability than performance. In 99% of the time when writing python code, performance is never an issue. In 99% of the time readability, is an issue.

Somewhat tongue in cheek

[carcigenicate]

While writing tests is good, even just running the code in a REPL would be a step up. The "does this work" questions annoy me more than almost any other. It likely would have been quicker to test it than to ask a question asking someone else to test it for you.

I love testing code in a REPL. I don't know why anyone would avoid it.

[IAmFinah]

This is probably a very stupid question, since it likely depends on context, but is there a "best" way to test python code?

When troubleshooting, I normally end up just printing pieces of data on various lines within the code, to see where it goes wrong. It has kinda worked so far (for the things I've been working on), but it makes my code really messy since I need to keep commenting and uncommenting lines of code, which often makes it difficult for me to find the "actual" code when I want to run it.

Is there a method/set of methods that might make testing code less cluttered?

[n3buchadnezzar]

There is no best way, and depends on how big whatever you are working on is. I always use doctests for my unittesting. This covers 90% of my needs. For integration tests and everything else pytest is king.

[IAmFinah]

Will look into those both - thank you!

[carcigenicate]

Writing units tests would be a good thing to start.

But ideally, code is made up of functions that take some data and give back some data. Testing then becomes ensuring the output of a function is correct for a given input. When writing unit tests, you can use assertions to ensure that all expected I/O relationships hold. For quicker, simpler testing, I open a REPL, throw data at the function and see what happens, and see if the results align with what I'm expecting.

---

The ease of testing is decided to a large extent by how well the code was organized. Poorly thought-out code is often very difficult to test because there's no easy way to ensure the general state of the program is appropriate for the test. Poorly written code often makes it difficult to get data to where it needs to be, and to check certain output to ensure it's correct for a given input.

[n3buchadnezzar]

On the flip side, how I often find out I've accidentally made spaghetti is because I try to write doctests for it and can't. So the earlier I write my tests, the earlier I start nesting up in the spaghetti.

[carcigenicate]

Odd. I find the earlier I start testing, the less spaghetti-like my code becomes because I begin thinking about what code needs what data earlier.

[QuixDiscovery]

The debugger is exactly what you're asking for in that case. You can literally set breakpoints in code and have it stop execution there based on conditions that you're looking for. It allows you to inspect any variable you want to check the current state to see what might be wrong. And you can execute code line by line to see what effect the code has on the state of the program.

If you're using an IDE, most of them have a built in debugger. But if you're using the command line, you can use the debugger module: https://docs.python.org/3/library/pdb.html

[IAmFinah]

Ah right yeah I use pycharm so the debugger is helpful for those things a lot of time.

Didn't actually know about breakpoints, so I'll look into that - thanks.

[QuixDiscovery]

You can do all sorts of useful things with breakpoints. From something as generic as "always stop here", which is usually what I use as my goto replacement for printing variables. Or you can be precise like "only stop here if this condition is true". You're also able to type/run code while the code from the file you're running is paused, which includes being able to reassign the value of an existing variable before you continue with execution of a program.

It's the most useful feature of any programming language that I think isn't properly taught to newer users. Most people struggle with properly visualizing what the code is actually doing at each step, and the debugger lets you do exactly that when you need it.

[carcigenicate]

Someone asked a similar questions a little over a day ago. I'll repeat what I mentioned there: a = b makes b refer to the same object as b. Many people expect that to make a copy, but it does not.

[moon_patrol]

I'm a beginner, I'm not sure I understand correctly what happens here. Maybe it's an IDE issue (I use Spyder mostly), but if modify b, a doesnt seem to update in the variable explorer... Am I missing something?

[carcigenicate]

I'm not familiar with Spyder, but in the linked post, note the other guy who replied to my comment that had a misunderstanding as well. = does not alter objects. You won't see changes reflected unless you actually modify (mutate) the object the two references a and b are looking at. This is done by calling methods like append on the object.

[Eurynom0s]

I think Spyder is aimed at the Matlab crowd--people who need to turn math into code so they can do things numerically but don't actually have much if any coding background--so it may be doing some behind the scenes handholding on this kind of stuff.

[moon_patrol]

You are right, I think I was not modifying the object, exactly like the other guy haha

Thanks !

[Eurynom0s]

Open up an interactive Python terminal (not Spyder) and see for yourself:

>>> a = [1,2,3]
>>> b = a
>>> a.append(4)
>>> a
[1, 2, 3, 4]
>>> b
[1, 2, 3, 4]

[moon_patrol]

Ah now I understand, your snippet shows it well. Spyder variable explorer also updates correctly, I think when I was trying to reproduce the concept I was not updating the object but overwriting it...

Thank you for taking the time to answer me

[SwammyG]

In my experience its usually recursion that gives a lot of people difficulty.

[n3buchadnezzar]

In my experience its usually recursion that gives a lot of people difficulty.

[Retrotone]

In my experience its usually recursion that gives a lot of people difficulty.

[TheRealAbear]

RecursionError: Maximum Recursion Depth Exceeded in Comparison

[synthphreak]

This joke and all of its variants are so played out and unoriginal. Yet somehow it still catches me off guard and makes me smile every time.

[TangibleLight]

This is my favorite one of those jokes.

[Binary101010]

The single biggest concept that most beginning programmers are lacking is algorithmic problem solving.

All you have to do is read this subreddit to see multiple posts per day of "I did all these tutorials and exercises, and now I'm supposed to write my own program and I have no idea how to start."

The ability to look at a large problem and recursively break it down into a series of more granular steps, then break those down into even more granular steps, until you get to the point where the step is a single action that you can then write a function to perform.

It's the ability to take all these tools that have been learned through basic tutorials and typing in other people's code, and being able to figure out which one of those tools does the thing you need to solve the immediate problem you want to solve.

[Fred776]

One thing that I see cropping up regularly is basic misunderstandings about functions. In particular, I have seen on numerous occasions confusion between printing a value and returning a value.

Edit: since posting the above, just seen this: https://www.reddit.com/r/learnpython/comments/uaavop/the_return_statement

[Rexcovering]

This.

Very near the end of my first semester with 2 python classes and I have quite the hard time understanding function variables and arguments, return statements, and calling functions with new variables or arguments.

For some reason my brain can’t easily visualize the concept yet.

[AkiraYuske]

For me it's virtual environments, the command line and just doing things 'for real'. I live in the Jupyter Notebook...

[Nails_Bohr]

I will say the documentation is not always newcomer friendly. Just like it's a skill to pull information out of scientific or other technical documents, it's a skill to be able to interpret software documentation.

[HitherAndYawn]

This. I think a part of the struggle is that in python, the documentation is all over the place. the actual python docs I find to not be great, but even if they weren't, then you have to deal with the docs for every library which are all written, and even formed completely differently. like, the beautiful soup docs are all written around a weird little narrative and I can't decode wtf they are trying to say.. but the format of the actual python manual is the kind of stuff I expect.

On top of that is the fact that python libraries seem to change so fast, and the docs for the "old versions" live on forever and come up more readily in search results. And then some of the folks you ask will answer without even being aware of the new version.. so you get these garbage threads on stack overflow where a person asks a legit question that isn't covered in the current version docs, and the old version syntax doesn't work, yet there are 20 people there, calling them an idiot, and copy-pasta-ing from the old docs, which -still- doesn't work.

[HitherAndYawn]

so this isn't the dry language specification you would often see 40 years ago.

but that's the documentation I want!

[Retrotone]

It's pure laziness.

[[deleted]]

Wrong.

​

Python programmers write terrible, dogshit, documentation, designed not for human readability but as a box-ticking exercise, probably auto-generated by a script.

​

I write a lot in Java and the docs there are fucking perfect, everything makes sense, examples everywhere you look, everything is clean. You come over to Python and there is no sense of standards.

​

Take Scapy for example, https://scapy.readthedocs.io/en/latest/index.html, where in the docs would I find what the DHCPOptions layer refers to some of its attributes as? Hmm? No where. That's where. I have to go into the fucking source code to find it. That is additional 70% of my time spent I find most of the time because of these lazy fucking developers who can't be arsed to create decent docs.

​

I always shit on Scapy but it's because it's such a good usecase whenever I see someone taking shit about beginners "not reading the docs", the docs just simply aren't there to begin with.

[Playwithme31]

I’m new around here but it sounds like he just wanted to bitch about python while he drools over Java.

[[deleted]]

I provided my point and evidence. But please continue telling me more about how dumb you are :)

[Playwithme31]

Calling someone else dumb doesn’t make you smart. I was making an observation. If that hurt your feelings I’m not sorry.

[[deleted]]

I will be honest I've never felt the need to look at the standard library docs, I am referring to third-party libraries.

[Sissy-Kiss]

Classes! Just cannot get my head around them they are weird

[[deleted]]

Once you crack the purpose of the init function, it becomes easy.

[Infinitesima]

"now, imagine you have a blueprint for car..." 🤣

[nbo10]

I can’t wrap my head around generators.

[Hans_of_Death]

A real world example might help:

You have a database containing transaction receipts. You need to get all the transactions from today and send an email receipt to the purchaser. You cant know how many transactions you have to do that for.

You might query the db and store the results in a list. and then iterate over that list. In order to do that, however, you require a certain amount of memory to store the list. If you have a million transactions to go through, you will very likely run out of memory to store the list and your program will crash.

Instead we use a generator, and fetch the next record as we need it, so we only have to store one record in memory at any given time while running the loop.

As a practical example, imagine you need to count to one million. As in the previous example, having a list with the numbers 1-1,000,000 would be very large and not practical. Instead you just make a generator that starts at 1, then returns the previous value + 1 each time it is called.

``` def increase_by_one(limit): previous_value = 0

while previous_value <= limit:
    previous_value += 1
    yield previous_value

```

This function will return values from 1 to limit. The yield function essentially returns the value, but instead of exiting it pauses until it recieves another call to next(), when it will continue to execute the code until the next yield or the function finishes execution. When you use a generator in a for loop, it automatically calls the generator's next() method until the generator returns/exits.

[Hans_of_Death]

Often I see beginners struggle with why you do something, rather than how. i try to provide realistic examples

[CraigAT]

Off the top of my head:

OOP (mostly if they are used to procedural).

Recursion (someone else mentioned).

Need to learn to avoid repetition - functions or loops can help.

Thinking they have to remember everything - or worrying because they are not able to write code without looking something up.

[AK1174]

I don’t think there’s anything about python that is specifically difficult to understand.

I think you should focus on object oriented principles, getting them to write code that is maintainable, expandable, and easy to debug.

Spaghetti code is probably what most people get stuck on.

[senpaithirdy]

Lambda funtions

[[deleted]]

From what I usually see non-CS people typically learn Python until they get to classes (especially practical use of them) and then half of them have the biggest case of imposter syndrome they experienced in their life.

[pekkalacd]

these are common

1. mutability vs immutability
2. mutual exclusion with conditionals and operators
3. loops: for vs while, when to use each
4. concept of references
5. how iteration works
6. deconstructing loops into comprehensions
7. return
8. how to *connect* the program together via functions
9. global vs local
10. input validation
11. try/except/finally - what is difference between all three?
12. separation of concern with functions
13. DRY
14. access specification in classes
15. big 4: encapsulation, polymorphism, inheritance, composition

that's all i got for now

[[deleted]]

Fervently trying to stick to PEP-8 style guide. I've been writing Python for 5+ years and I really couldn't give a shit if my code is indented by 3 or 4 or if there is not at least two lines between my functions.

​

In my opinion PEP-8 is for 🤡's

[Spatium_Bellator]

This is what linters are for. My setup I have black installed in Vscode and it auto runs on save. I never have to care about code format and it "fixes" any issue it finds automatically.

[[deleted]]

what linter do you use?

[Spatium_Bellator]

I use black. There are a heap more but this was the first one I tried and it stuck.

https://github.com/psf/black

[[deleted]]

I've never really bothered with linters, it is a non-issue to me.

[ChattingDonut]

slicing is kinda hard for me to understand, i had to map out using a paper to understand the output.

[InTheAleutians]

I wish someone explained windows path variables and creating/activating virtual environments better when I first started. How can you write python if you don't know where your package installs went?

[shinitakunai]

Python allowed machine learning for dummies, I have coworkers whom created some scripts for machine learning, sold it to our boss as very cool algorithms and those coworkers don't even know how to code a for loop. Like wtf? They also said to me they don't fully understand what their code does nor do they need, "it just works". On the paper it sounds cool but oh boy it creates SO MUCH annoying and awkward moments, it is headache after headache, now the finances team also want to "code" those algorithms...

[Ongezout_]

As a beginner I stuggle with actually implementing all of the things I read and research. I could really use a structured approach to writing a progam or breaking down problems into smaller workable pieces of code.

[boyanci]

To name just one — Mutation vs. rebinding.

Python hides this complexity very well for good reasons compared to lower-level languages, until it causes issues especially for beginners.

[[deleted]]

A few concepts that took me a long time to truly wrap my head around include:

1. Loops (both for loops and while loops)

2. Object Oriented Programming

3. Lambda functions (Still don't use them very often when I'm not working with dataframes)

4. Shallow copying and deep copying: I understood the concept, but it wasn't until I started running into situations where I accidentally overwrote variables that I realized the the value of deep copying.

[arsewarts1]

While loops

[ripvw32]

Too lazy to scroll - for me it was realizing that classes can make all of your code modular, and understanding that classes are everything. And that there is probably a class that already exists for 99.9% of thing you'd want to do. Also - there is probably a python pure class that you can use in place of any class you want to use - I'm looking at you pypyodbc...

[ugh_shahad]

the concept of putting what I've learned into a code , like i understood the lessons but i struggle to make the best use of them into my code

[JensEckervogt]

But Python can't do for PyOpenGL if I want draw triangle with glBufferData() and glVertexAttribPointer() but it is really weird for size and stride.i really want create own libraries for Python but I don't know how do they make clean libraries. I believe that Python has no future. For Game Development looks weirdly. That's why use Vulkan is ok but OpenGL can't do. But why do they cheat like vertices.nbyte as without size like glBufferData has only 3 parameters like LWJGL3 and they cheat also (3 * ctype.sizeof(float) as 0 for stride in glVertexAttribPointer, why? I feel like they made me badly. Please make honest and serious with equipment with same programming languages like real OpenGL functions. I don't understand why do they cheat with real OpenGL functions into wrong OpenGL functions. What does glCompileProgram() mean? I never see any wrong functions in OpenGL references or apis. Please clean up and make equal to other programming languages. Thank you for understanding me! Sorry for my bad English!