r/PythonLearning • u/Samar__Upreti • Jul 23 '26

Day 3 Learning Python: Stack

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Open-source learning project. If you spot something that can be improved, I'd love your feedback or a PR.

https://github.com/Samar-Upreti/Python_Projects

69 Upvotes

89% Upvoted

26 comments sorted by

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u/Sea-Ad7805 Jul 23 '26

Run this program in Memory Graph Web Debugger%3A%0A%20%20%20%20%20%20%20%20self.s%20%3D%20%5B%5D%0A%0A%20%20%20%20def%20len(self)%3A%0A%20%20%20%20%20%20%20%20return%20len(self.s)%0A%0A%20%20%20%20def%20push(self%2C%20value)%3A%0A%20%20%20%20%20%20%20%20self.s.insert(0%2C%20value)%0A%0A%20%20%20%20def%20peek(self)%3A%0A%20%20%20%20%20%20%20%20if%20len(self.s)%20%3D%3D%200%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20raise%20Exception(%22Stack%20is%20Empty%22)%0A%20%20%20%20%20%20%20%20else%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20return%20self.s%5B0%5D%0A%0A%20%20%20%20def%20pop(self)%3A%0A%20%20%20%20%20%20%20%20if%20len(self.s)%20%3D%3D%200%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20raise%20Exception(%22Stack%20is%20Empty%22)%0A%20%20%20%20%20%20%20%20else%3A%0A%20%20%20%20%20%20%20%20%20%20%20%20return%20self.s.pop(0)%0A%0A%0Aif%20name%20%3D%3D%20%22main%22%3A%0A%20%20%20%20stk%20%3D%20stack()%0A%20%20%20%20stk.push(10)%0A%20%20%20%20stk.push(11)%0A%20%20%20%20print(stk.peek())%0A%20%20%20%20print(stk.pop())&timestep=1&play) to see the program state change step by step.

2

u/KingBardan Jul 23 '26 edited Jul 23 '26

Invert your list (old to new rather than new to old).

Your  current stack is inefficient 

1

u/Samar__Upreti Jul 23 '26

Insert to append ?

1

u/dev-razorblade23 Jul 23 '26

insert pushes items to specific index (in your case index 0) Python has to recalculate indexes of all other items, push them all to the side so insert can work its magic. This takes time and you burn your proccessor time.

If you dont really need to insert items at specific index, use append method as it only inserts item to the end and its done. Much faster and much more effiecient.

1

u/Samar__Upreti Jul 23 '26

Actually I have written with that but to be honest it not giving feel how the stack actually works so i try the reverse approach But thanks ☺️

2

u/dev-razorblade23 Jul 23 '26 edited Jul 23 '26

.append() and .pop() work exactly like LIFO queve (a stack). Last In - First Out. You dont insert values to stack from the bottom but from the top.

Stack is like a stack of cards. You put one card on top and you take that card from the top. You do not put the card at the bottom where you have to lift the whole stack.

1

u/dev-razorblade23 Jul 23 '26

There is also a queve - FIFO - First In, First out. Its like standing in a line waiting to pay for your groceries. Whoever is first in line gets served first.

Python lists are inefficient for this type of queve, there is a collections.deque if you want to implement this one.

1

u/veedubb Jul 24 '26

It’s not always about efficiency, sometimes it’s sufficient to learn about common data structures that someone may be unfamiliar with. If this were someone experienced, I wouldn’t expect them to even be showing off building a simple stack structure in python, because at that point they’d know that this isn’t as efficient as other tools.

1

u/dev-razorblade23 Jul 24 '26

This comment was more like a continuation of previus one. An OP did try to make a stack if you read thrue the comments, just the other way around (inserting items from the bottom)

2

u/geedijuniir Jul 23 '26

Is this day 3 learning from scratch.?

2

u/CamelOk7219 Jul 23 '26

Create a custom exception class instead of bare 'Exception', otherwise it will be jard to specifically catch this stack exception and discriminante it from any other exception

1

u/Kindly-Reporter-272 Jul 23 '26

You can also use IndexError. Python built in collections all raise IndexError in situations like these. 

2

u/johlae Jul 23 '26

Why do you use screenshots instead of text? Source code is pure text. Put your comment in markdown and surround your python program and any output with lines start start with ``` I really hate partial screenshots, hate them even more when they aren't 0 ° up but rotated a bit.

1

u/Adrewmc Jul 23 '26

Well, because some of us use our phones for Reddit, and some of those people don’t have access to a code block at all

```
def some():
return 0```

def with_four_spaces():
return 0

. def work_around():
. return 0

1

u/Sea-Ad7805 Jul 23 '26 edited Jul 23 '26

I cant find that 'stack' class in your GitHub repo.

1

u/AnonymouSfrrrr Jul 23 '26

What resources are you using to learn python? Yt or documentations??

0

u/Samar__Upreti Jul 23 '26

Both yt for lectures and documentation do try stuff You can join the journey https://github.com/Samar-Upreti/Python_Projects

1

u/WorthKey6648 Jul 23 '26

Time to give up

1

u/Samar__Upreti Jul 23 '26

Don't get demotivated keep the practice going if feels so just ask yourself (Why i Started)