List methods in Python

List methods in Python

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]
  

   

• 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 10087 List.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 List1 List1.extend(List2)         print(List1)   # Add List1 to List2 now List2.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'
  

• 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
  

• 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
  

• 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
  

• 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
  

• 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
  

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 True List.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
  

• 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]

• 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]

Last Updated on November 13, 2021 by admin