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Lists in python

Lists are used to store multiple items. List items are ordered, changeable, and allow duplicate values. List items are indexed, the first item has index [0], the second item has index [1] etc. Lists also have negative index number starting from [-1] from the last element of the list.

Example of list with numbers

li=[10,20,30,40,50]
print(li)



Output

[10, 20, 30, 40, 50]



Example of list with float

 

li=[10.23,20.12,30.34,40.21,50.32]
print(li)


Output

[10.23, 20.12, 30.34, 40.21, 50.32]



Example of list with string

courses=["python","c","c++","java","oracle"]
print(courses)


Output

['python', 'c', 'c++', 'java', 'oracle']



Example of list containing values of different types

li=[10,20.12,"python"]
print(li)


Output

[10, 20.12, 'python']



Example of list using for loop

li=[10,20,30,40,50]
for i in li:
    print(i,end=' ')


Output

10 20 30 40 50



Example of list using positive index number

li=[10,20,30,40,50]
print(li[1])


Output

20



Example of list using negative index number

li=[10,20,30,40,50]
print(li[-1])


Output

50



Example of joining lists

lst1=[10,20,30]
lst2=[40,50,60]
lst3=lst1+lst2
print(lst3)


Output

[10, 20, 30, 40, 50, 60]


List slicing




Example1 of list slicing

li=[10,20,30,40,50]
print(li[1:4])


Output

[20, 30, 40]





Example2 of list slicing

li=[10,20,30,40,50]
print(li[:])


Output

[10, 20, 30, 40, 50]





Example3 of list slicing

li=[10,20,30,40,50]
print(li[2:])


Output

[30, 40, 50]





Example4 of list slicing

li=[10,20,30,40,50]
print(li[:4])


Output

[10, 20, 30, 40]


Example5 of list slicing

li=[10,20,30,40,50]
print(li[1:-2])


Output

[20, 30]


Declare an Empty List in Python

Declaring an empty list in python can be achieved in two ways:

  1. By using square brackets[]
  2. By using the list() constructor

Create an Empty List in Python using Square Brackets []

To declare an empty list just assign a variable with square brackets.
Example: 

# Code to declare empty list
mylist=[]	
print("Values of mylist:", mylist)
print("Type of mylist:", type(mylist))
print("Size of mylist:", len(mylist))

Output

Values of mylist: []
Type of mylist: <class 'list'>
Size of mylist: 0


Create an Empty List using the list() Constructor

The list() constructor is used to create a list in Python.

# Program to create empty list 
# list is declared using constructor()
mylist=list()  
print("Values of mylist:",mylist)
print("Type of mylist:",type(mylist))
print("Size of mylist:",len(mylist))

Output

Values of mylist: []
Type of mylist: <class 'list'>
Size of mylist: 0


Python Append to Empty List

In Python, we can create an empty list and then later append items to it, using the Python append() function.

# create an empty list
mylist= []
 
# append items to an empty list
mylist.append(100)
mylist.append(200)
mylist.append(300)
mylist.append(400)
 
print("Values of mylist:",mylist)
print("Type of mylist:",type(mylist))
print("Size of mylist:",len(mylist))

Output

Values of mylist: [100, 200, 300, 400]
Type of mylist: <class 'list'>
Size of mylist: 3