Exploring List
List is similar to an array but lists can store different types of elements.
Lists are represented by a square bracket
student = [ 101 , ‘abc’ , 50 ]
First element is student [ 0 ] which is 101 and so on.
print ( student [ 0:3 ] ) will display [101, 'abc', 50]
print ( student [ 0 : 3 : 2 ] ) will display [ 101, 50 ] with step of 2 that is student[0].. Student[2] …
Creating lists using range() function
Range function is used as range( start, stop, stepsize ) By default stepsize is 1
for n in range ( 0, 10, 2 ) :
print ( n ) // it will print 0,2,4,6,8
Creating list
lst = list( range( 0,10,2 ) )
print( lst )
Creating lists using range() function
Printing the list using while loop
n=0
while n < len( lst ):
print( lst [n] )
n=n+1
Printing the list using for loop
for n in lst :
print ( n )
Updating the elements of the list
The lists are mutable means we can append, update or delete the contents of the list.
lst = list( range( 1, 5 ) )
Append() function appends a new element at the end of list
lst.append( 8 )
Update the contents of the list
lst [0] = 9
lst [ 1: 3 ] = 10, 11
[0] [1] [2] [3] [4]
Concatenation of two lists
‘+’operator is used to concate two list
Lst1=[1,2,3]
Lst2=[‘a’,’b’]
Lst3=lst1+lst2
Print(lst3)
Repetition of lists
We can repeat the elements of a list ‘n’ number of times using ‘*’ operator.
Lst=[1,2,3]
Print(lst*2)
Membership in lists
We can check is an element is a member of list or not with use of membership operator.
If the element is in list then it returns true when we use ‘in’ operator else it returns false.
If the element is not in the list then the ‘not in’ operator returns true else returns false.
Aliasing and Cloning lists
Provide another name to existing list is called aliasing a list.
If l1 is existing list then,
l2=l1 will create an alias of the l1. here l1 and l2 both refer to same memory location
Obtaining exact copy of the existing list is called cloning list.
If l1 is existing list then,
L2=l1[:] will create clone of l1. here l1 and l2 both are different and store on different memory location.
Example:
#list
student=[101,'abc',50]
print(student)
print(student[0:3])
print(student[0:3:1])
print(student[0:3:2])
#create list from range
for n in range(0,10,2):
print(n)
lst=list(range(0,10,2))
print(lst)
#printing list using while loop
n=0
while n<len(lst):
print(lst[n])
n=n+1
#printing list using for loop
print("List with for loop")
for n in lst:
print(n)
#updating the elements of list
lst=list(range(1,5))
print(lst)
lst.append(8)
print(lst)
del lst[0]
print(lst)
lst.remove(8)
print(lst)
lst.reverse()
print(lst)
#concatenatoion of two list
l1=[1,2,3]
l2=['a','b']
l3=l1+l2
print(l3)
#Repetition of list
l4=l3*2
print(l4)
#membership in list
m_lst=[10,20,30,40]
x=int(input("enter element"))
if x in m_lst:
print(x, "is present in list")
else:
print(x, "is not present in list")
#alias and cloning the list
print("Alias")
l1=[1,2,3,4,5]
l2=l1
print("l1 is", l1)
print("l2 is", l2)
l2[0]=20
print("l1 is", l1)
print("l2 is", l2)
print("Cloning")
l1=[1,2,3,4,5]
l2=l1[:]
print("l1 is", l1)
print("l2 is", l2)
l2[0]=20
print("l1 is", l1)
print("l2 is", l2)
Methods to process List
|
Method |
Example |
Desciption |
|
Sum() |
List.sum() |
Return sum of all elements |
|
Index() |
List.index(a) |
Return first occurrence of a in list |
|
Append() |
List.append(a) |
Append a at the end of list |
|
Insert() |
List.insetr(I,a) |
Insert a in the list at I index |
|
Sort() |
List.sort() |
Sort in ascending order |
|
Pop() |
List.pop() |
Removing the ending element of list |
|
Remove() |
List.remove(a) |
Remove a from the list |
|
Count() |
List.count(a) |
Return number of occurrence of a in list |
|
Extend() |
List.extends(list1) |
Append list1 to list |
|
Copy() |
List.copy() |
Copies all the list elements into a new lsit and returns it |
|
Reverse() |
List.reverse() |
Reverse the elements of list |
|
clear() |
List.clear() |
Clear the list elements |
Example:
l1=[1,2,3,4,5,6,7]
print(l1);
print("Sum method", sum(l1))
print("length method", len(l1))
print("Index of 5 in list",l1.index(5))
l2=[6,7]
l1.append(l2)
print("append method", l1)
l1.append(8)
print("append method", l1)
l1.insert(0,99)
print("after insert method", l1)
l3=l1.copy()
print("copy method", l3)
l4=[10,20]
l4.extend(l1)
print("extend method", l4)
print("count method 1 in list1", l1.count(1))
l4.remove([6,7])
print("remove method", l4)
l5=[1,2,3,4,5,6,7]
print("pop method", l5.pop())
l5.reverse()
print("reverse method", l5)
l5.sort()
print("sort method")
print(l5)
l5.clear()
print("Clear method")
print(l5)
Nested Lists
We can write list within another list and it is called nested list.
L1=[1,2,3]
L2=[4,5,6,l1]
Example:
l1=[1,2,3]
l2=[4,5,6,l1]
print("list 1",l1)
print("list 2",l2)
print("Complete list")
for i in l2:
print(i)
print("Elements from nested list")
for i in l2[3]:
print(i)
Output:
('list 1', [1, 2, 3])
('list 2', [4, 5, 6, [1, 2, 3]])
Complete list
4
5
6
[1, 2, 3]
Elements from nested list
1
2
3
