Python – Lists

In Python – Lists are a sort of data container that may hold numerous pieces of information in a single variable. It can include components of several data kinds. A list’s elements are sorted and may be retrieved using an index number.

Create List

A Python – Lists may be made by using a comma to separate the components and surrounding them with square brackets []. It may also be made with the help of the list() function and list comprehension.

#List with multiple datatypes
Info = ['John', 25, 'London']  
print(Info)

#Creating list using list function
colors = list(('Red', 'Blue', 'Green')) 
print(colors)

#Creating list using list comprehension
x = [1, 2, 3, 4, 5]
y = [i*i for i in x]    
print(y)

The output of the above code will be:

['John', 25, 'London']
['Red', 'Blue', 'Green']
[1, 4, 9, 16, 25]

Access element of a List

The index number of a list element can be used to access it. The index number in Python begins with 0 in the forward direction and -1 in the reverse direction. The indexing notion of a list is depicted in the diagram below.

List Indexing:

Python Lists Indexing

The following example shows how to use the index number to retrieve elements of a Python – Lists.

weekday = ['MON', 'TUE', 'WED', 'THU', 'FRI']

#forward indexing
print(weekday[1]) 

#backward indexing 
print(weekday[-1])

The output of the above code will be:

TUE 
FRI

Access range of elements of a List

A statement like [startIndex: endIndex] can be used to pick a range of entries from a list, with end index being omitted. If start index and end index aren’t specified, the first and last index numbers in the list will be used instead.

weekday = ['MON', 'TUE', 'WED', 'THU', 'FRI']
print(weekday[1:3])
print(weekday[-5:-1],"\n")

print(weekday[1:])
print(weekday[:-3],"\n")

print(weekday[:])

The output of the above code will be:

['TUE', 'WED']                         
['MON', 'TUE', 'WED', 'THU']            

['TUE', 'WED', 'THU', 'FRI']            
['MON', 'TUE']                          

['MON', 'TUE', 'WED', 'THU', 'FRI']

Modify the value of an Element

To update the value of an element, use its index to assign a new value.

Info = ['John', 25, 'London'] 
#value at index=0 changed to 'Marry'
Info[0] = 'Marry'  
print(Info)

The above code will give the following output:

['Marry', 25, 'London']

Add elements in a List

To add elements to a list, use the techniques listed below:

  • append() – add an element to the end of a list.
  • insert() – insert an element at the specified index of the list.
days = ['MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT']
# add this element in last of the list
days.append('SUN')   
print(days)

month = ['JAN', 'FEB', 'MAR', 'MAY']
# add 'APR' at index=3 of the list
month.insert(3,'APR') 
print(month)

The output of the above code will be:

['MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT', SUN']
['JAN', 'FEB', 'MAR', 'APR', 'MAY']

Delete elements of a List

To remove elements from a list, use the methods/keywords listed below:

  • remove() – deletes the first occurrence of a specified element from the list.
  • pop() – deletes element at specified index or last element if index is not specified.
  • clear() – deletes all elements of a list.
  • del – deletes an element or range of elements or list itself.
number = [10, 50, 50, 100, 1000]
#delete first occurrence of 50.
number.remove(50)    
print(number)

number = [10, 50, 50, 100, 1000]
#delete element at index=3.
number.pop(3)        
print(number)

number = [10, 50, 50, 100, 1000]
#delete last element from the list.
number.pop()        
print(number)

number = [10, 50, 50, 100, 1000]
#delete all elements from the list.
number.clear()     
print(number)

The above code will give the following output:

[10, 50, 100, 1000]
[10, 50, 50, 1000]
[10, 50, 50, 100]
[]

 

The del keyword is used to delete an element or range of elements or list itself.

number = [10, 50, 50, 100, 1000]
#delete element at index=3.
del number[3]       
print(number)

number = [10, 50, 50, 100, 1000]
#delete element at index=1,2 and 3.
del number[1:4]     
print(number)

number = [10, 50, 50, 100, 1000]
#delete list 'number'.
del number          
print(number)

The above code will give the following output:

[10, 50, 50, 1000]
[10, 1000]

Traceback (most recent call last):
  File "Main.py", line 14, in <module>
    print(number)
NameError: name 'number' is not defined

List Length

To determine the total number of entries in a list, tuple, set, or dictionary, use the len() function.

number = [10, 50, 50, 100, 1000, 1000]
print(len(number))

The output of the above code will be:

6

Loop over List

For loop over List:

for loop can be used to access each element of a list.

colors = ['Red', 'Blue', 'Green']
for x in colors:
    print(x)

The output of the above code will be:

Red
Blue
Green

While loop over List

Each member of a list may be retrieved using the while loop and the len() method.

colors = ['Red', 'Blue', 'Green']
i = 0
while i < len(colors):
    print(colors[i])
    i = i + 1

The above code will give the following output:

Red Blue Green

Check an element in the List

If the control statement is used to determine whether or not the list includes the supplied element.

colors = ['Red', 'Blue', 'Green']
if 'white' in colors:
  print('Yes, white is an element of colors.')
else:
  print('No, white is not an element of colors.')

The above code will give the following output:

No, white is not an element of colors.

Copy List

There are a few options for making a copy of the list.

  • = operator: Creates a reference of the list. Any change in old list modifies new list also.
  • copy(): Creates an independent copy of a list.
  • list(): Creates an independent copy of a list.
colors = ['Red', 'Blue', 'Green']
mycolor = colors
yourcolor = colors.copy()
hiscolor = list(colors)

print(mycolor)     
print(yourcolor)   
print(hiscolor, "\n")    

#delete last element in 'colors'
colors.pop()       

print(mycolor)     
print(yourcolor)   
print(hiscolor)

The output of the above code will be:

['Red', 'Blue', 'Green']      
['Red', 'Blue', 'Green']      
['Red', 'Blue', 'Green']      

['Red', 'Blue']               
['Red', 'Blue', 'Green']      
['Red', 'Blue', 'Green']      

Join Lists

There are a few different methods to join a list.

  • + operator: Used to join two lists into a new list.
  • append(): Appends all elements of one list into another.
  • extend(): Adds all elements of one list into another.
colors = ['Red', 'Blue', 'Green']
numbers = [10, 20]
mylist1 = colors + numbers
print(mylist1)

colors = ['Red', 'Blue', 'Green']
numbers = [10, 20]
for i in numbers:
  colors.append(i)
print(colors)

colors = ['Red', 'Blue', 'Green']
numbers = [10, 20]
colors.extend(numbers)
print(colors)


The output of the above code will be:

['Red', 'Blue', 'Green', 10, 20]  
['Red', 'Blue', 'Green', 10, 20]  
['Red', 'Blue', 'Green', 10, 20]

Also Read: Java – Continue Statement

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