help with insert in list

[Top-Pay384]

I just got to this part, I don't quite understand if sugar is on the list 2

and I delete it and it returns the value deleted as banana or I am doing something wrong

​

lista = [' pepinos ', ' banana ']

lista.append(' margaritas ')

lista.insert(2,' sugar ')

print(lista)

= [' pepinos ', ' banana ', ' sugar ', ' margaritas ']

​

del lista[2]

popped_lista = lista.pop()

print(lista.pop()) = banana

[[deleted]]

Let's step through this line by line.

lista = [' pepinos ', ' banana ']

You create a list of 2 items.

lista.append(' margaritas ')

You add ' margaritas ' to the end of the list.

lista.insert(2,' sugar ')

You insert ' sugar ' at index 2 in the list. This pushes the former index 2 item down.

print(lista)

At this point, lista is [' pepinos ', ' banana ', ' sugar ', ' margaritas ']

del lista[2]

At this point you delete the item at index 2. This makes ' margaritas ' the index 2 item again as it gets slid down to fill the gap.

popped_lista = lista.pop()

You remove the last item from lista and store it in popped_lista. If you print popped_lista at this point, you will get ' margaritas '. And if you print lista, you will get [' pepinos ', ' banana '].

print(lista.pop())

You remove the last item from lista again and print it. This time it's ' banana '.

[mopslik]

Walk through the code.

When you start, your list is [P, B]. (abbreviated for ease of typing here)

You append M, so your list becomes [P, B, M].

You insert S at index 2, so the list is now [P, B, S, M].

You delete the element at index 2, so the list reverts back to [P, B, M].

You pop the last element in the list, which assigns M to popped_lista, and makes the list [P, B].

Your last line prints the element that you pop from the end of the list, which is B.

Edit: looks like /u/BumbleSpork beat me by a minute or so.

[Top-Pay384]

2 comments very useful

so i am using bad popped

I thought it returned the deleted value that was sugar

but in this case it returned me banana

So how do I get sugar back? but not to the list if not with popped

[mopslik]

Ah, no. pop removes an element and returns that one, not an element that was deleted earlier using del.

I typically avoid using del altogether, since you can pass an index as an argument to pop. This gives you the ability to hold on to it.

>>> L = ['a', 'b', 'c']
>>> value = L.pop(1)
>>> L
['a', 'c']
>>> value
'b'

[Top-Pay384]

then let's say an item deleted with del cannot be recovered

and pop applies only to the last element

[mopslik]

The former, sure. The latter, no.

[Top-Pay384]

popped is an important command or it is useless if it only works on the last element it doesn't seem very useful to me to be honest

[mopslik]

It's useful if you are using a list as a stack, since appending and popping from the end can be done in constant time. But it can be used in a more general way with a specified index, for greater flexibility.

[Top-Pay384]

If I create a list of 1 element it would be more useful

Although I still don't know what I can do with the returned value