Stacks are often known as LIFO (Last In First Out) structure. It means the data will enter into it at the end , and the last data will come out first. The easiest example can be of couple of marbles in an one side closed pipe. So if you want to take the marbles out of it you have to do that from the end where you entered the last marble. To achieve the same in code

>>> a
[1, 2, 3, 4, 5, 6]
>>> a.pop()
6
>>> a.pop()
5
>>> a.pop()
4
>>> a.pop()
3
>>> a
[1, 2]
>>> a.append(34)
>>> a
[1, 2, 34)

We learned a new method above pop(). pop(i) will take out the ith data from the list.

In our daily life we have to encounter queues many times, like in ticket counters or in library or in the billing section of any supermarket. Queue is the data structure where you can append more data at the end and take out data from the beginning. That is why it is known as FIFO (First In First Out).

>>> a = [1, 2, 3, 4, 5]
>>> a.append(1)
>>> a
[1, 2, 3, 4, 5, 1]
>>> a.pop(0)
1
>>> a.pop(0)
2
>>> a
[3, 4, 5, 1]

To take out the first element of the list we are using a.pop(0).