List methods in Python

This article is extension of below articles :
Python List
List 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)
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    # Adds List Element as value of List.
    List = ['Mathematics', 'chemistry', 1997, 2000]
    List.append(20544)
    print(List)

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    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.

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    List = ['Mathematics', 'chemistry', 1997, 2000]
    # Insert at index 2 value 10087
    List.insert(2,10087)     
    print(List)        

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    Output:

    ['Mathematics', 'chemistry', 10087, 1997, 2000, 20544]
    
  • extend(): Adds contents to List2 to the end of List1.
    Syntax:

    List1.extend(List2)
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    List1 = [1, 2, 3]
    List2 = [2, 3, 4, 5]
      
    # Add List2 to List1
    List1.extend(List2)        
    print(List1)
      
    #Add List1 to List2 now
    List2.extend(List1) 
    print(List2)

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

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    Output:

    15
    

    What happens if numeric value is not used a parameter?
    Sum is calculated only for Numeric values, elsewise throws TypeError.
    See example:

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    List = ['gfg', 'abc', 3]
    print(sum(List))

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    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)
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    List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]
    print(List.count(1))

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    Output:

    4
    
  • length:Calculates total length of List.
    Syntax:

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

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    Output:

    10
    
  • index(): Returns the index of first occurrence. Start and End index are not necessary parameters.
    Syntax:

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

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    Output:

    1
    

    Another example:

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    List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]
    print(List.index(2,2))

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    Output:

    4
    
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    List = [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]
      
    # will check from index 2 to 3.
    print(List.index(2,2,4))    

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    Output:

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

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    Output:



    1.054
    
  • max(): Calculates maximum of all the elements of List.
    Syntax:

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

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

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    Output:

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

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    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.



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

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    Output:

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

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    Output:

    2.3
    
  • del() : Element to be deleted is mentioned using list name and index.
    Syntax:

    del list.[index]
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    List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]
    del List[0]
    print(List)

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

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    Output:

    [2.3, 4.445, 5.33, 1.054, 2.5]
    

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