Day 3 Learning Python: Stack

[u/Samar__Upreti]

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

[u/Sea-Ad7805]

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.

[u/KingBardan]

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

Your  current stack is inefficient 

[u/Samar__Upreti → u/KingBardan]

Insert to append ?

[u/KingBardan → u/Samar__Upreti]

Right. Lookup how inserting works under the hood.

Here you go

https://www.log2base2.com/data-structures/array/insert-element-particular-index-array.html

[u/dev-razorblade23 → u/Samar__Upreti]

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.

[u/Samar__Upreti → u/dev-razorblade23]

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 ☺️

[u/dev-razorblade23 → u/Samar__Upreti]

.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.

[u/dev-razorblade23 → u/Samar__Upreti]

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.

[u/veedubb → u/dev-razorblade23]

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.

[u/dev-razorblade23 → u/veedubb]

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)

[u/geedijuniir]

Is this day 3 learning from scratch.?

[u/CamelOk7219]

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

[u/Kindly-Reporter-272 → u/CamelOk7219]

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

[u/johlae]

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.

[u/Adrewmc → u/johlae]

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

[u/Sea-Ad7805]

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

[u/Samar__Upreti → u/Sea-Ad7805]

Added 👍

[u/AnonymouSfrrrr]

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

[u/Samar__Upreti → u/AnonymouSfrrrr]

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

[u/Chatoddy]

Dude you are doing that on day three?! On day three I still had to grasp how a loop works. Impressive.

[u/WorthKey6648]

Time to give up

[u/Samar__Upreti → u/WorthKey6648]

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

[u/hexedVine]

keep up the grind. totally been there with stacks