Internal list processing in Python

We can create a list in Python like below.

Example :

We can access each element of a list in Python at its assigned index. In Python, the starting index of the list sequence is 0, and the ending index (if there are N elements) is N-1.

Also, as shown above, array lists also have a negative index, starting at -N (if there are N items in the list) to -1.

Viewing list items in Python :
Individual list items can be accessed through their indexes, as shown in the following code snippet.

list1 = [ 1 , 2 , 3 , 4 ]

list1 = [ 1 , 2 , 3 , 4 ]

 
# for print only one item from the list

print (list1 [ 1 ])

  
# print the sequence of items in the list
# we use the value & # 39;: & # 39; before it starts
# and the value after that indicates the end of the sequence

print (list1 [ 1 : 4 ])

 
# access via negative index

print (list1 [ - 1 ])

Purpose and data access:
To create a list, we need to specify the elements in square brackets & # 39 ; [] & # 39; and then give it a name. Whenever you want to access the elements of a list, use that list name and the index of the element you want to show. 
Each element in the list is assigned an index in positive indexing, we have an index from 0 to the end of the list, and in negative indexing, we have an index from -N (if the elements are N) to -1. 
As shown in the examples above, accessors are handled manually. We can also access or assign elements through loops.

# assigning items to the list

list1 = []

for i in range ( 0 , 11 ):

  list1.append (i)

 
# access to items from the list

for i in range ( 0 , 11 ):

print (list1 [i])

Updating the list:
We can update already assigned items in the list, and we can also add one item at a time to your list. Even though you can expand your list by adding another list to the current list. 
The above task can be accomplished as follows.

list1 = [ 1 , 2 , 3 , 4 ]

 
# update

list1 [ 2 ] = 5

print (list1)

 
# adding

list1.append ( 6 )

print (list1)

 
# extension

list1 .extend ([ 1 , 2 , 3 ])

print (list1)

Note: append () and extension () are built in python for lists.

Removing list items:
We can remove items in lists using the del function. In this, you need to specify the position of the element, which is the index of the element, and this element will be removed from the list, and the index will be updated.


In the above image, item 3 in index 2 was removed and the index was updated after that.

list1 = [ 1 , 2 , 3 , 4 , 5 ]

print (list1)

 
# remove element

del list1 [ 2 ]

print (list1)

Time complexity of operations

Operation

Average Case

Amortized Worst Case

Copy O (n) O (n)
Append [1 ] O(1) O(1)
Pop last O (1) O (1)
Pop intermediate

O (k)

O (k)

Insert

O (n)

O (n)

Get Item O (1)

O (1)
Set Item O (1) O (1)
Delete Item O (n) O (n)
Iteration O(n) O(n)
Get Slice O (k)

O (k)
Del Slice O (n) O (n)
Set Slice O (k + n) O (k + n)
Extend [1] O (k) O (k)
Sort O (n log n) O (n log n)
Multiply O (nk)

O (nk)
x in s O (n) O (n)
min (s), max (s) O (n) O (n)
Get Length

O (1)

O (1)

Source: Python Wiki

Python list and its operations.