In this section, you will learn to create and update a list in Python programming. Further, you will learn how to slice a list in Python.
Create a List:
A list can be created by using square brackets
. The elements of a list are placed inside square brackets, and are separated from each other by a comma
,. The elements of a list could have different data types.
l =  # empty list l = [2, 4, 6, 8] # elements of same data type l = [2, 'Python', 1+2j] # elements of different data type
You can also create a nested list, that is list inside another list.
l = [[2,4,5], 'python']
Access List Elements:
The following are some of the way using which you can access list elements:
You could use index to access elements of a list. The index of a list starts from 0.
>>> x = [2, 4, 6, 8, 10] >>> print('x =', x) # display the first element x = 2 >>> print('x[0:2] =', x[0:2]) # display the first two elements of list that is at location 0 and 1 x[0:2] = [2, 4] >>> print('x[2:] =', x[2:]) # display elements from location 2 (third element) x[2:] = [6, 8, 10]
The list element can be modified (updated, deleted, added) because
list is mutable. If the index is outside of the list index range, you will have an
It is allowed to use negative indexes to access elements in the list. For example, index
-1 refers to the last element. Similarly, index
-2 refers to the second last item.
>>> l = [2, 4, 6, 8, 10] >>> print(l[-1]) 10 >>> print(l[-2]) 8 >>> print(l[-3]) 6
Slice a List in Python:
A slicing operator
: is used to extract a range of elements from a list.
>>> l = [2, 4, 6, 8, 10] >>> print(l[1:3]) # print from location 1 to 3 [4, 6] >>> print(l[:2]) # print from beginning to location 2 [2, 4] >>> print(l[2:]) # print elements from location 2 onwards [6, 8, 10] >>> print(l[:]) # print the entire list [2, 4, 6, 8, 10]
Add Elements to a List:
You can use the list method
append() to append an item to the end of a list.
>>> l = [1, 3, 5, 7, 9, 11] >>> l.append(13) >>> print(l) [1, 3, 5, 7, 9, 11, 13]
append(x) adds the item x as one item to the list.
extend(x) method is the right method to extend the list by appending all the items in the given object
>>> l = [1, 3, 5, 7, 9, 11] >>> l.extend([13, 14, 15]) >>> print(l) [1, 3, 5, 7, 9, 11, 13, 14, 15]
extend() method, you could concatenate two lists by using
>>> l = [2, 4, 6, 8, 10] >>> print(l + [12, 14, 16]) [2, 4, 6, 8, 10, 12, 14, 16]
You could use
insert(i, x) method to insert the element
x to the given index
>>> l = [2, 4, 6, 8, 10] >>> l.insert(2, 0) >>> print(l) [2, 4, 0, 6, 8, 10]
Delete Elements From a List:
del statement deletes one or more items from a list. You can also use
delto delete the entire list:
>>> l = [2, 4, 6, 8, 10] >>> del l >>> print(l) [2, 4, 6, 8] >>> del l[0:2] >>> print(l) [6, 8] >>> del l >>> print(l) Traceback (most recent call last): print(l) NameError: name 'l' is not defined
After a list is deleted by
del l, referencing this list
l is an error.
If you want to clear a list then you can also use
The following table describes the list methods:
||add an item to the end of the list|
||add more than one items to a list. It works by adding elements of a list to another list (in which you want to add elements).|
||add an element at a desired location.|
||remove a particular item from the list.|
||remove an item from a given location and returns that item.|
||remove all elements from the list.|
||return the index of the first matched element in the list.|
||return the total number of items passed|
||sort elements of a list in ascending order.|
||reverse the order of the elements of the list.|
||return a copy of an already existing list.|
List Membership Check:
in keyword checks if an element is a member of the list or not.
>>> l = [2, 4, 6, 8, 10] >>> print(5 in l) False >>> print(2 in l) True
List Elements Iteration:
You can iterate through a list by using
l = [2, 4, 6, 8, 10] for i in l: print(i)
2 4 6 8 10
Built-in Functions Applicable to List:
The following table is the collection of built-in functions that can be used with lists to perform different tasks:
||return the index and the value of all the elements of the list as a tuple. It returns an
||return the number of items in a list or the length of the list.|
||convert a sequence (tuple, set, string, dictionary) to list.|
||return the maximum number in the list.|
||return the minimum number in the list.|
||return a sorted list.|
||return the sum of all elements of the list.|