Introduction to List

Lists:

•          A list is a data structure in Python that is a mutable (changeable).
•          The list values are assigned by placing them within square braces ([ ]) and separating them by commas and each value is identified by an index.
•          An index is an integer variable or value that indicates an element of a list.

To declare a list, the syntax is :

<Name of list> = [value1,value2,value3,value4,………. valueN]

For example :

Num=[3,32,56,78,65]                                                           # A list with integer values

Mobile=[‘Samsung’, ‘Nokia’, ‘Vivo’, ‘Redmi’, ‘Oppo’]         # A list with string

Elist =[ ]                                                                              # An empty list

Accessing List of Elements

For example:

>>> Num=[3,32,56,78,65]                                # A list with integer values

>>>print(“The list is :”,Num)

How to Display List Elements?

         

0	1	2	3	4
Samsung	Nokia	Vivo	Redmi	Oppo

Source Code:

Mobile=['Samsung', 'Nokia', 'Vivo', 'Redmi', 'Oppo']

print("Print List elements are :", end=" ")

for i in Mobile:

    print(i, end=" ")

output :

Source Code

0	1	2	3	4
3	32	56	78	65

Num=[3,32,56,78,65]

print("Print List elements are :", end=" ")

for i in Num:

    print(i, end=" ")

Concatenating Lists

Concatenating means joining two operands by linking  them end-to-end.Using + operator concatenate two lists with each other and produce a third list. for example

>>>X= [43,55,67]

>>>Y=[32,65,87]

>>>Z=X+Y

>>>print(Z)

[43,55,67,32,65,87]

Replicating a List

List can be replicated or repeated or repeatedly concatenated with the asterisk operator '*'. 

For example :

>>>aList=[11,22,33]

>>>print((aList*2) #list aList repeats two times.

[11,22,33,11,22,33]

>>>Student=['Sachin','Divy','Yashi']

>>>print(Student*2)    #list Student repeats two times

 ['Sachin','Divy','Yashi,'Sachin','Divy','Yashi']

List in Membership operators:

• in. The in operator tests whether an element is a member of a list or not. If the element is a member in the list, then it will produce True otherwise False. For Example:

>>> Student=['Satyam','Arif', 'Adil','Deepak','Harshita','Ruku']

>>> 'Deepak' in Student

True

>>> 'Riya' in Student

False

• not in. The not in operator evaluates to true if it does not find the element in the list and otherwise false. For example :

        >>> 'Deepak' not in Student

        False

        >>> 'Riya' not in Student

        True

Slicing the Lists:

Syntax : Seq=aList [start:stop:step]

  aList[strat:stop:step] creates a list slice out of list aList with elements falling between indexes start and stop, not including stop, skipping step-1 elements in between.

Nested Lists : A list inside another list is called nested list or matrix. For example

        # Accessing nested list

        aList=[21,43,54,[65,76],87,98]

        print(aList)

        print("2nd element :",aList[1])

        print("3rd element :",aList[3])

        print("3rd of 1st element :",aList[3][0])

# print list address with element

                Marks=[76,87,54,98,43,67,32]

                Length=len(Marks)

                for i in range(Length):

                print("Marks[",i,"]->",Marks[i])

1.    Write a program to print a list Num in reverse order.

                Where, Num=[3,32,56,78,65]

Source Code

Num=[3,32,56,78,65]

ln=len(Num) # length of list

c=-1

print("Original List\tReverse List")

for i in range(0,ln):

    print(Num[i],"\t:\t",Num[c])

    c=c-1

 2. Write a program input number from the keyboard and search element.

Source Code:

aList=eval(input("Enter the value of list :"))

Search=int(input("Enter the value to be search :"))

length=len(aList)

flag=False

for i in range(length):

    if(Search==aList[i]):

        flag=True

        break

if(flag):

    print(Search,' value position is ',i  )

else:

    print(Search, " is not found")

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