Lists

A list is a data structure, that is mutable (or changeable). List items are placed inside square brackets[].
Important thing about a list is that the items in a list need not be of the same type.

Creating a List: The following example shows how to create list.

list1 = [10, 20, 30, 40, 50]
print(list1)

[10, 20, 30, 40, 50]

Accessing List Values: To access list values, use index or indices of an element. Indexes starts from 0, index value of 1^st element is 0, 2^nd element is 1 and so on. Python also supports negative indexes which are count from right.

list1 = [10, 20, 30, 40, 50]
print("Value at index 2 is:",list1[2])
print("Value at index -2 is:",list1[-2])

Value at index 2 is: 30
Value at index -2 is: 40

Updating List:You can modify the elements in the list. You can add new elements in a list with append() method.

list1 = [10, 20, 30, 40, 50]
print("Value at index 2 is:",list1[2])
list1[2] = 25
print("New value at index 2 is:",list1[2])

Value at index 2 is: 30
New value at index 2 is: 25

Deleting Element from List: Using del statement you can remove element from list.

list1 = [10, 20, 30, 40, 50]
print("Original list is:",list1)
del list1[2]
print("After deleting an element list is:",list1)

Original list is: [10, 20, 30, 40, 50]
After deleting an element list is: [10, 20, 40, 50]

Basic List Operations:

1. + Concatenate two lists and result is a new list.

   list1 = [10, 20, 30]
   list2 = [40, 50]
   print("list1 + list2 is ",list1+list2)
   

   list1 + list2 is [10, 20, 30, 40, 50]
   

2. * Repetition of list for N times and result is a new list.

   list1 = [10, 20, 30]
   print("list1 * 2 is ",list1*2)
   

   list1 * 2 is [10, 20, 30, 10, 20, 30]
   

3. in Membership operator which returns True when element present in list. False otherwise.

   list1 = [10, 20, 30]
   print("20 in list1 ",20 in list1)
   print("40 in list1 ",40 in list1)
   

   True
   False
   

4. [start:stop:step] Gives access to a specified range of sequence’s elements.

   list1 = [10, 20, 30, 40, 50]
   print("list1[::] is",list1[::])
   print("list1[2:] is",list1[2:])
   print("list1[:3] is",list1[:3])
   print("list1[::-1] is",list1[::-1])
   

   list1[::] is [10, 20, 30, 40, 50]
   list1[2:] is [30, 40, 50]
   list1[:3] is [10, 20, 30]
   list1[::-1] is [50, 40, 30, 20, 10]
   

List Methods:

1. append()
2. clear()
3. copy()
4. count()
5. extend()
6. index()
7. insert()
8. pop()
9. remove()
10. reverse()
11. sort()

Practice Programs

• Read list elements from the user.
  

  n = int(input("Enter number element to be insert: "))
  list1 = []
  print("Enter {} elements".format(n))
  for i in range(n):
      list1.append(int(input()))
  print("List is",list1)
  

  Enter number element to be insert: 5
  Enter 5 elements
  1
  3
  2
  5
  4
  List is [1, 3, 2, 5, 4]
  

• Read list elements from the user using map() function.
  

  n = int(input("Enter number element to be insert: "))
  print("Enter {} elements".format(n))
  list1 = list(map(int, input().split()))[:n]
  print("List is",list1)
  

  Enter number element to be insert: 5
  Enter 5 elements
  1 3 2 5 4
  List is [1, 3, 2, 5, 4]