Lists

In Python, a list is a mutable sequence data type that can store a collection of values of any data type, including other lists.
Lists are ordered, meaning the order in which items are added to the list is preserved.
They are indexed, meaning each item can be accessed by its index in the list.

>>> my_list = [1,2,3, 'four', 'five']
>>> my_list
[1, 2, 3, 'four', 'five']

List Methods of Python

1. Inserting data using .append(x) :-

This method appends the given element x at the end of the list.

>>> my_list.append(6.75)
>>> my_list
[1, 2, 3, 'four', 'five', 6.75]

2. Inserting from an iterable using .extend(iterable_data_type) :-

.extend() accepts an iterable and adds all its elements at the end of the list.

>>> my_tuple = ('seven' , 8, 9, 10.11)
>>> my_list
[1, 2, 3, 'four', 'five', 6.75]
>>> my_list.extend(my_tuple)
>>> my_list
[1, 2, 3, 'four', 'five', 6.75, 'seven', 8, 9, 10.11]

3. .insert(i, x) :-

This method inserts an item at a specific position in the list.

>>> my_list
[1, 2, 3, 'four', 'five', 6.75, 'seven', 8, 9, 10.11]
>>> my_list.insert(0, 0)
>>> my_list
[0, 1, 2, 3, 'four', 'five', 6.75, 'seven', 8, 9, 10.11]

4. .remove(x) :-

This method removes the first occurrence of an item x from the list.
If not present in the list it throws an error.

>>> my_list
[0, 1, 2, 3, 'four', 'five', 6.75, 'seven', 8, 9, 10.11]
>>> my_list.remove('five')
>>> my_list
[0, 1, 2, 3, 'four', 6.75, 'seven', 8, 9, 10.11]
>>> my_list.remove('five')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: list.remove(x): x not in list

5. .pop(i) :-

The .pop() method removes and returns the item at a specific position in the list. If no index is specified, it removes and returns the last item.
example:-

>>> my_list
[0, 1, 2, 3, 'four', 6.75, 'seven', 8, 9, 10.11]
>>> my_list.pop()
10.11
>>> my_list.pop()
9
>>> my_list
[0, 1, 2, 3, 'four', 6.75, 'seven', 8]
>>> my_list.pop(0)
0
>>> my_list
[1, 2, 3, 'four', 6.75, 'seven', 8]

6. index(x) :-

This method returns the index of the first occurrence of an item in the list.
You can specify a starting and/or ending index for the search.
example:-

>>> my_list = [1, 2, 3, 'four', 6.75, 'seven', 8]
>>> my_list.index(3)

7. count(x) :-

The .count() method returns the number of times an item appears in the list.

>>> my_list = [1, 2, 3, 'four', 6.75, 'seven', 8,3,3]
>>> my_list.count(3)
3

8. .sort() :-

The .sort() method sorts the items in ascending order.

>>> my_list
[1, 2, 3, 8, 3, 3]
>>> my_list.sort()
>>> my_list
[1, 2, 3, 3, 3, 8]

9. .reverse() :-

The .reverse() method is used to reverses the order of items in the list.

>>> my_list
[1, 2, 3, 3, 3, 8]
>>> my_list.reverse()
>>> my_list
[8, 3, 3, 3, 2, 1]

10. .copy() :-

This method will returns a copy of the list.

>>> my_list
[8, 3, 3, 3, 2, 1]
>>> my_copied_list = my_list.copy()
>>> my_copied_list
[8, 3, 3, 3, 2, 1]

Using Lists as Stacks

In Python, list can be directly usable as a stack(“last-in, first-out”).

to add an element to the top of the stack use append() method

and remove element from the top of the stack use pop() method.

Example:

>>> stack = [1,2,3,4]
>>> stack.append(5)
>>> stack.append(6)
>>> stack
[1, 2, 3, 4, 5, 6]
>>> 
>>> 
>>> stack.pop()
6
>>> stack
[1, 2, 3, 4, 5]

Using Lists as Queues

In Python, it is also possible to use list as a queue (“first-in, first-out”) ,for that we need to use append()method for inserting element and pop(0) for deleting element in the queue .However it is not the efficient way beacuse every time we delete a element from first position ,means we need to left shift by 1 for all the remaining elements.

To implement a queue, use collections.deque which was designed to have fast appends and pops from both ends.

Example:

>>> from collections import deque
>>> 
>>> queue = deque([1,2,3,4])
>>> queue
deque([1, 2, 3, 4])
>>> 
>>> 
>>> queue.append(5)
>>> queue
deque([1, 2, 3, 4, 5])
>>> 
>>> queue.popleft()
1
>>> queue
deque([2, 3, 4, 5])