List methods in Python

07 Jun, 2022
This article is extension of below articles :Python ListList Methods in Python | Set 1 (in, not in, len(), min(), max()...)List Methods in Python | Set 2 (del, remove(), sort(), insert(), pop(), extend()...)
Adding and Appending
append(): Used for appending and adding elements to List.It is used to add elements to the last position of List.Syntax:  list.append (element)# Adds List Element as value of List.List = ['Mathematics', 'chemistry', 1997, 2000]List.append(20544)print(List)Output:['Mathematics', 'chemistry', 1997, 2000, 20544]
 
 list.append (element)
# Adds List Element as value of List.List = ['Mathematics', 'chemistry', 1997, 2000]List.append(20544)print(List)
Output:
['Mathematics', 'chemistry', 1997, 2000, 20544]

 
insert(): Inserts an elements at specified position.Syntax: list.insert(<position, element)Note: Position mentioned should be within the range of List, as in this case between 0 and 4, elsewise would throw IndexError.List = ['Mathematics', 'chemistry', 1997, 2000]# Insert at index 2 value 10087List.insert(2,10087)     print(List)        Output:['Mathematics', 'chemistry', 10087, 1997, 2000, 20544]

 list.insert(<position, element)
Note: Position mentioned should be within the range of List, as in this case between 0 and 4, elsewise would throw IndexError.
List = ['Mathematics', 'chemistry', 1997, 2000]# Insert at index 2 value 10087List.insert(2,10087)     print(List)        
Output:
['Mathematics', 'chemistry', 10087, 1997, 2000, 20544]

extend(): Adds contents to List2 to the end of List1.Syntax:List1.extend(List2)List1 = [1, 2, 3]List2 = [2, 3, 4, 5]  # Add List2 to List1List1.extend(List2)        print(List1)  # Add List1 to List2 nowList2.extend(List1) print(List2)Output:[1, 2, 3, 2, 3, 4, 5]
[2, 3, 4, 5, 1, 2, 3, 2, 3, 4, 5]
List1.extend(List2)
List1 = [1, 2, 3]List2 = [2, 3, 4, 5]  # Add List2 to List1List1.extend(List2)        print(List1)  # Add List1 to List2 nowList2.extend(List1) print(List2)
Output:
[1, 2, 3, 2, 3, 4, 5]
[2, 3, 4, 5, 1, 2, 3, 2, 3, 4, 5]
sum(), count(), index(), min() and max() functions of List
sum() : Calculates sum of all the elements of List.Syntax: sum(List)List = [1, 2, 3, 4, 5]print(sum(List))Output:15
What happens if numeric value is not used a parameter?Sum is calculated only for Numeric values, elsewise throws TypeError.See example:List = ['gfg', 'abc', 3]print(sum(List))Output:Traceback (most recent call last):
  File "", line 1, in 
    sum(List)
TypeError: unsupported operand type(s) for +: 'int' and 'str'

 sum(List)
List = [1, 2, 3, 4, 5]print(sum(List))
Output:
15

What happens if numeric value is not used a parameter?Sum is calculated only for Numeric values, elsewise throws TypeError.See example:
List = ['gfg', 'abc', 3]print(sum(List))
Output:
Traceback (most recent call last):
  File "", line 1, in 
    sum(List)
TypeError: unsupported operand type(s) for +: 'int' and 'str'

count():Calculates total occurrence of given element of List.Syntax:List.count(element)List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(List.count(1))Output:4

List.count(element)
List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(List.count(1))
Output:
4

length:Calculates total length of List.Syntax:len(list_name)List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(len(List))Output:10

len(list_name)
List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(len(List))
Output:
10

index(): Returns the index of first occurrence. Start and End index are not necessary parameters.Syntax:List.index(element[,start[,end]])List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(List.index(2))Output:1
Another example:List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(List.index(2,2))Output:4
List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]  """index(element, start, end) : It will calculate till index end-1. """  # will check from index 2 to 4.print("After checking in index range 2 to 4")print(List.index(2,2,5))  # will check from index 2 to 3.print("After checking in index range 2 to 3")print(List.index(2,2,4))     Output:After checking in index range 2 to 4
4
After checking in index range 2 to 3
Traceback (most recent call last):
  File "", line 1, in 
    List.index(2,2,4)
ValueError: tuple.index(x): x not in tuple

List.index(element[,start[,end]])
List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(List.index(2))
Output:
1

Another example:
List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]print(List.index(2,2))
Output:
4

List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]  """index(element, start, end) : It will calculate till index end-1. """  # will check from index 2 to 4.print("After checking in index range 2 to 4")print(List.index(2,2,5))  # will check from index 2 to 3.print("After checking in index range 2 to 3")print(List.index(2,2,4))     
Output:
After checking in index range 2 to 4
4
After checking in index range 2 to 3
Traceback (most recent call last):
  File "", line 1, in 
    List.index(2,2,4)
ValueError: tuple.index(x): x not in tuple

min() : Calculates minimum of all the elements of List.Syntax:min(List)List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(min(List))Output:1.054

min(List)
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(min(List))
Output:
1.054

max(): Calculates maximum of all the elements of List.Syntax:max(List)List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(max(List))Output:5.33

max(List)
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(max(List))
Output:
5.33

sort() and reverse() functions
reverse(): Sort the given data structure (both tuple and list) in ascending order. Key and reverse_flag are not necessary parameter and reverse_flag is set to False, if nothing is passed through sorted().Syntax:sorted([list[,key[,Reverse_Flag]]])
 list.sort([key,[Reverse_flag]])List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]  #Reverse flag is set TrueList.sort(reverse=True)   #List.sort().reverse(), reverses the sorted list  print(List)        Output:[5.33, 4.445, 3, 2.5, 2.3, 1.054]
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]sorted(List)print(List)Output:[1.054, 2.3, 2.5, 3, 4.445, 5.33]

sorted([list[,key[,Reverse_Flag]]])
 list.sort([key,[Reverse_flag]])
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]  #Reverse flag is set TrueList.sort(reverse=True)   #List.sort().reverse(), reverses the sorted list  print(List)        
Output:
[5.33, 4.445, 3, 2.5, 2.3, 1.054]

List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]sorted(List)print(List)
Output:
[1.054, 2.3, 2.5, 3, 4.445, 5.33]

Deletion of List Elements
To Delete one or more elements, i.e. remove an element, many built in functions can be used, such as pop() & remove() and keywords such as del.
pop(): Index is not a necessary parameter, if not mentioned takes the last index.Syntax: list.pop([index])Note: Index must be in range of the List, elsewise IndexErrors occurs.List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(List.pop())Output:2.5
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(List.pop(0))Output:2.3

 list.pop([index])
Note: Index must be in range of the List, elsewise IndexErrors occurs.
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(List.pop())
Output:
2.5

List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]print(List.pop(0))
Output:
2.3

del() : Element to be deleted is mentioned using list name and index.Syntax:del list.[index]List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]del List[0]print(List)Output:[4.445, 3, 5.33, 1.054, 2.5]
del list.[index]
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]del List[0]print(List)
Output:
[4.445, 3, 5.33, 1.054, 2.5]
remove(): Element to be deleted is mentioned using list name and element.Syntax: list.remove(element)List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]List.remove(3)print(List)Output:[2.3, 4.445, 5.33, 1.054, 2.5]

 list.remove(element)
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]List.remove(3)print(List)
Output:
[2.3, 4.445, 5.33, 1.054, 2.5]

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