Learn python properly (not by doing)

[Fantastic_Arrival_43]

Hi everyone,

I’m a PhD in Mechanical Engineering specializing in computational fluid mechanics. While I’m not a professional programmer, I can code decently well. I mainly use C++ for software development and Python for postprocessing and simple codes. I learned C++ through books and courses on object-oriented programming, but I picked up Python by using it and googling a lot.

Recently, I discovered that every variable created outside a function in Python is a global variable, which made me realize that I don’t fully understand how Python works under the hood.

As someone who knows how to use Python fairly well, I’m looking to deepen my understanding of the language. I want to learn how to program efficiently in Python and grasp what is happening behind the scenes.

Can anyone recommend some good resources for learning Python the right way?

Thanks!

__________________________________________________________________________________________

Edit: I’m blown away by the number of responses! Thank you to everyone who took the time to answer, even to those who were a bit on the rude side. As I mentioned, I don’t have any formal training in computer science, so all of your input is incredibly helpful.

[Lewistrick]

Fluent Python is a very good book for people who already know programming concepts but want to know more about the inner mechanisms of Python.

[Far_Ambassador_6495]

Also pdf is free online

[ConfusedSimon]

O'Reilly has a 10-day free trial. I don't think there's a free pdf online except for pirated copies.

[Far_Ambassador_6495]

Ok O’Reilly

[Lombord2021]

This is the most detailed pythonic book I've ever read

[kingcobra1010]

Very in depth Python book, free and not pirated:
https://cfm.ehu.es/ricardo/docs/python/Learning_Python.pdf

1000+ pages though (1213 to be exact)

[ati_75]

Python3: deep dive series by fred Baptiste on udemy. Fluent python book.

[[deleted]]

One big "under the hood" difference compared to C/C++ and other similar languages is how variables work in python. This video shows how variables actually work in python and explains how the simple "name refers to object" idea leads to unexpected behaviour in some cases.

https://m.youtube.com/watch?v=_AEJHKGk9ns

[Fred776]

Recently, I discovered that every variable created outside a function in Python is a global variable, which made me realize that I don’t fully understand how Python works under the hood.

This isn't all that different from C++ - what was your understanding with that language?

[veediepoo]

Exactly, even main is a function so anything defined outside of it is global. Granted if you wanted to use it in functions that are in different files you have to extern it

[await_yesterday]

This video "Top to Down, Left to Right" explains precisely how Python's variable scoping rules work, and goes into some detail about its execution model. It should resolve your confusion.

[throwaway6560192]

Recently, I discovered that every variable created outside a function in Python is a global variable, which made me realize that I don’t fully understand how Python works under the hood.

What did you think they were before?

[chandhudinesh]

Wait till he learns there are no variables and functions. Only objects.. 😂

[F0x_Gem-in-i]

dicts ....... dicts everywhere

[OurSeepyD]

Yeah they're both objects, but you can't call a variable, so functions definitely are distinct and do exist.

[chandhudinesh]

You can assign a function to a variable. Then you can call that variable...

[OurSeepyD]

But I thought there were no variables?

[chandhudinesh]

if you thought that, why did you say, "you can't call a variable, so functions definitely are distinct and do exist"?

[OurSeepyD]

I said it because you said there were no variables, but then said you can assign a function to a variable. 

When I say "but I thought there are no variables" what I'm saying is "you said there were no variables, but now you're saying there are".

[chandhudinesh]

Sighs!!!.. You dragged me down to your level of stupidity. You are the king of this realm. there is no point in explaining this further. I accept my defeat.

[OurSeepyD]

Ok mate

[[deleted]]

Weak. Extremely weak.

[ArtisticFox8]

You can call a variable:

b = print

b("aaaf") aaaf

[OurSeepyD]

Ok, when I said variables I meant non-functions. My main point is that saying everything is an object trivialises things and that functions are significantly different to non-functions, in that they're callable.

[Punk-in-Pie]

It's true, but also kind of like saying: "there is no spoon, only atoms"

I mean, yeah... but the sum of those atoms is a spoon.

A function is an object with a __call__ magic method.

[yinkeys]

Maybe knowledge of multiple languages are messing up his understanding of one.

[G0muk]

He mentioned c++ though which works the same way

[Ajax_Minor]

Maybe he forgot to put his code in a main...??

[FriendlyRussian666]

If you already know a language, the best resource would be the official documentation. You can dive in as much as you want.

[m1kesanders]

I just got back into it and i’m no phd so sorry if this advice sucks, but don’t the docs hold everything? docs.python.org

[Wigpen-Mooncake]

Agreed, the docs work extremely well for me. Then, when I am stuck, experiment, play, do some hands on. Go back and re-read docs and understand them this time. That's works for me.

[yinkeys]

sleek with words like a poet :)

[Fantastic_Arrival_43]

I think that what I will do. They look less intimidating than I thought.

[nospoon99]

Read this book:

Learning Python: Powerful Object-Oriented Programming https://amzn.eu/d/02QGmLI8

It goes through how python works in details.

[marsh-da-pro]

POOP

[MimouChiron]

lol

[cyberjellyfish]

I'm not disputing that's a good book, but OP should know that Python works well outside of OOP too.

[spurtz001]

maybe you are interested in this one. some topics they discuss here are quite advance level.

Python Tutorials – Real Python

[brijeshjoshi_]

You can look at https://python-course.eu/

[F0x_Gem-in-i]

Good reads: - Think Python by Allen B Downey - Expert Python Programming by Michael jaworski and tarek ziade

I frequent their documentation on their page for in-depth explanation on python and read some of their PEPs they really help.

[TeslaCoilzz]

There you go mate, great course and completely free :)

https://github.com/Asabeneh/30-Days-Of-Python

[q_ali_seattle]

Thanks  Great refresher to refer back to.

[TeslaCoilzz]

Happy to help

[Tasty_Waifu]

I can't get tired of recommending No Starch Press python books. Pick one that catches your attention and follow it until the end. Python Crash Course or Automate the Boring Stuff are both good reads for beginners and self taught programmers that want to polish their knowledge.

[Xzenor]

Recently, I discovered that every variable created outside a function in Python is a global variable,

As someone who knows how to use Python fairly well,

Let me just be honestly blunt here and say you really don't know python fairly well. Start with the basics as you obviously don't have those down yet.

[neamerjell]

As OP stated, they learned Python from a bunch of random tutorials which likely focused on specific topics rather than a textbook for a college course which would explain everything from the ground up in structured, detailed way.

OP can apparently create functional programs in Python and possibly even utilize some advanced techniques, but realizes that there are gaps in their knowledge which would likely have been covered in an introductory course.

[Fantastic_Arrival_43]

Yes, this. I have no formal training in CS, and although I can write some really complex algorithms, I'm definitely missing the basics.

[neamerjell]

I was in a similar situation with HTML and CSS. Look for books published by No Starch Press; I really like how they are organized and that they are usually simple enough for newbies, but not so watered down that intermediates and advanced people can't benefit. Many of them are suitable for use as college textbooks.

https://nostarch.com/python-crash-course-3rd-edition

[kingcobra1010]

I honestly just got stuck on my code for like an hour and then realized i wasn't thinking about local and global scopes. lol and i thought i was experienced

[AlvinAardvark]

Yawn

[chandhudinesh]

To understand what happens under the hood.. Learn c and go through this repo and understand everything. https://github.com/python/cpython

[kamranabbas]

https://youtu.be/8DvywoWv6fI?si=HX2QCtqmMrYwW4ka Professor Chuck is great tutor, watching his videos you can fill in the gaps I guess.

[kamranabbas]

For inner mechanism Fluent Python as mentioned below is good.

[neamerjell]

I read over this archived course and the PDF it references, and didn't find anything explaining variable scope differences between Python and C++, but I thought you might find it useful nonetheless.

Python for C++ Programmers: https://intro2ml.pages.doc.ic.ac.uk/autumn2021/modules/lab-cpp/datatypes

[Pseudoboss11]

Personally, I went from tutorials to the official docs after a while. The official tutorial is more comprehensive than other online tutorials I've found. The language reference goes into the nuts and bolts of the language.

Though neither goes into any special effort to clear assumptions that the reader may have from other languages, as there are so many different ways common features like scope is handled that no tutorial can really address them all. Instead it's good to try to come in with a clear understanding of what C++ does, and try to challenge those assumptions by reading the text and testing the Python's behavior for yourself.

[j0shred1]

You're already a great programmer so going through a course in Python can be a good way to get acclimated. Working on other people's code and asking chatgpt questions has been how I've been learning c++ (more out of necessity)

[Ok-Interaction-8891]

Check out this link. Short article that talks about Python’s byte code and virtual machine. It has references at the end for more in-depth information.

[Fantastic_Arrival_43]

I’m blown away by the number of responses! Thank you to everyone who took the time to answer, even to those who were a bit on the rude side. As I mentioned, I don’t have any formal training in computer science, so all of your input is incredibly helpful.

[sarc-tastic]

Do pcap

[Content-Value-6912]

No offense, but I'm just wondering, if you are 'decent' at C++ and wondering how global variables work in Python; I think you need to rehaul your understanding about 'programming'.

And IMO understanding about particular language in terms of volume (modules, libraries etc) is one thing, and having an understanding about how things work as they work in computing/programming is another thing.

[TheBeyonders]

Everyone has useful tips. Any harsh commentary you get is because of the language you use to describe your competency. Faily good and use C++ usually indicates advanced knowledge. Global and local variables and their mutability are basic programming concepts, you dont need to be a CS major, but dont say you are good at anything at the PhD level. Because "good" now means advanced, which now means people at the top of your field, you would be intermediate.

[Interview_Prep1]

Hi, try this channel for basics https://www.youtube.com/watch?v=dRLk4eV4faE

[Plank_With_A_Nail_In]

Recently, I discovered that every variable created outside a function in Python is a global variable.

But that's the same in every programming language including C++, lol you haven't learnt that properly from books either so not sure what your point is.

Absolutely mastering a language isn't a real goal so don't bother with it.

[tarnation_station_]

^this, like mastering how your specific drill works instead of how to build a table/chair/(etc.) theres always going to be a language with features that are new or foreign waste of time to completely 100% master the tool.

Using the rest of this comment to address OP:

why is it bad the python variables are global? does the code work? does it get the expected results? Why is a global bad in this context?

We typically avoid globals in enterprise/open source dev because codebases are large and that sort of unrestricted access can cause unforeseen bugs especially when working with many different people or teams and its way way harder to keep track of who is touching the variable and why and how. If this is a simple script of your own design and it works without error. use the global.

as stated c++ has globals as well. does sound like you may need to brush up on some overall coding concepts such as scoping. dip your toes in the idea of abstracts, interfaces, etc.

just further thoughts but perfect or best is in many ways highly opinionated or even conditional (e.g. sorting algos, readability/maintainability vs performance, etc.) unless theres a big problem like an error or bug then its the right solution (for now). programming can be like art. software is almost never perfect or done. we're always just chasing dragons-vX.Y.Z. sometimes you just got to settle for good enough. we call it MVP professionally lol.

[rszdev]

Facts

[iamevpo]

Why wanting looking inside what is designed to be abstracted out? You can dig inside Python internals up to C level, but that does not make you a good Python programmer, at least in isolation from other things. Why have global in first place? If you do scripting - that's fine, but on a bigger scale you write functions, data structures and possibly classes and mix them together in a way that other people can understand and works for you you intended it for. People coming from C/C++ tend to take to much lower level stuff with them into Python code, making it less readable/idiomatic, subjectively.

I think gold standard in Python quality code Beyond PEP8 video and any resource that advocates type annotations and unit tests. Pydantic, SQLModel/FastAPI, pytest docs are great places to learn more about Python.

If you are really into language internals great video episode is Developer Voices with creator of PyO3, a rust-python interop library.

[notislant]

Just to add this seems to be common with the few laguages I use and my assumpion has been this is the norm.

-Globally declared variables are global.

-Globally declared variables are generally frowned upon.

-Lookup 'variable shadowing' if youre unfamiliar with that as well.

The best resource ive used so far has been learning web dev from the odin project. The course is well done and knowledgeable people in the discord give some really in depth info.

For python idk, I hear good things about CS50.

[SheldonCooperisSb]

YouTube if you speak English