“Computer Science is a science of abstraction - creating the right model for a problem and devising the appropriate mechanizable techniques to solve it.”

– A. Aho and J. Ullman

4.1 Introduction to List

The data type list is an ordered sequence which is mutable and made up of one or more elements. Unlike a string which consists of only characters, a list can have elements of different data types such as integer, float, string, tuple or even another list. A list is very useful to group elements of mixed data types. Elements of a list are enclosed in square brackets and are separated by comma.

Example 4.1

#list1 is the list of six even numbers
>>> list1 =[2,4,6,8,10,12]
>>> print(list1)
[2,4,6,8,10,12]

#list2 is the list of vowels
>>> list2 = [‘a’,’e’,‘i’,‘o’,‘u’]
>>> print(list2)
[‘a’, ’e’, ‘i’, ‘o’, ‘u’]

#list3 is the list of mixed data types
>>> list3 = [100,23.5,‘Hello’]
>>> print(list3)
[100, 23.5, ‘Hello’]

#list4 is the list of lists called nested
#list
>>> list4 =[[‘Physics’,101],[‘Chemistry’,202],
[‘Mathematics’,303]]
>>> print(list4)_
[[‘Physics’, 101], [‘Chemistry’, 202],
[‘Mathematics’, 303]]

4.1.1 Accessing Elements in a List

Each element in list is accessed using value called index. The fist index value is 0, the second index is 1 and so on. Elements in the list are assigned index values in increasing order sterling from 0.

To access an element, use square brackets with the index [] value of that element. We may also use negative index value to access elements starting from the last element in the list, having index value - 0.

#initialing a list named list1
>>> list1 = [2,4,6,8,10,12]
>>> list1[0] #returns first element of list1
2
>>> list1[3] #returns fourth element of list1
8
#Out of range index value for the list returns error
>>> list1[15]
IndexError: list index out of range
#an expression resulting in an integer index
>>> list1[1+4]
12
>>> list1[-1] #return first element from right
12
#length of the list1 is assigned to n
>>> n = len(list1)
>>> print(n)
6
#Get the last element of the list1_
>>> list1[n-1]
12
_#Get the first element of list1 _
>>> list1[-n]
2

4.1.2 Lists are Mutable

In Python, lists are mutable. It means that the contents of the list can be changed after it has been created.

#List list1 of colors
>>> list1 = [‘Red’,‘Green’,‘Blue’,‘Orange’]
#change/override the fourth element of list1
>>> list1[3] = ‘Black’
>>> list1 #print the modified list list1
[‘Red’, ‘Green’, ‘Blue’, ‘Black’]

4.2 List Operations

The data type list allows manipulation of its contents through various operations as shown below.

4.2.1 Concatenation

Python allows us to join two or more lists using concatenation operator using symbol + .

Concatenation is the merging of two or more values. Example: we can concatenate strings together.

#list1 is list of first five odd integers
>>> list1 = [1,3,5,7,9]
#list2 is list of first five even integers
>>> list2 = [2,4,6,8,10]
#Get elements of list1 followed by list2
>>> list1 + list2
[1, 3, 5, 7, 9, 2, 4, 6, 8, 10]
>>> list3 = [‘Red’,‘Green’,‘Blue’]
>>> list4 = [‘Cyan’, ‘Magenta’, ‘Yellow’
,‘Black’]
>>> list3 + list4
[‘Red’,‘Green’,‘Blue’,‘Cyan’,‘Magenta’,
‘Yellow’,‘Black’]

Note that, there is no change in original lists i.e., list1, list2, list3, list4 remain the same after concatenation operation. If we want to use the result of two concatenated lists, we should use an assignment operator.

For example,

#Join list 2 at the end of list
>>> new List = list 1 + list 2
[1, 3, 5, 7, 9, 2, 4, 6, 8, 10]

>> new list The concatenation operator ‘+’ requires that the operands should be of list type only. If we try to concatenate a list with elements of some other data type, TypeError occurs.

>>> list1 = [1,2,3]
>>> str1 = “abc”
>>> list1 + str1
(TypeError: can only concatenate list (not “str”) to list)

4.2.2 Repetition

Python allows us to replicate the contents of a list using repetition operator depicted by symbol *.

>>> list1 = [‘Hello’]
#elements of list1 repeated 4 times
>>> list1 * 4
[‘Hello’, ‘Hello’, ‘Hello’, ‘Hello’]

4.2.3 Membership

The membership operator in checks if the element is present in the list and returns True, else returns False.

>>> list1 = [‘Red’,‘Green’,‘Blue’]
>>> ‘Green’ in list1
True
>>> ‘Cyan’ in list1
False

The Operator not in transpose returns True if the element is not present in the list, else it returns False.

>>> list1 = [‘Red’,‘Green’,‘Blue’]
>>> ‘Cyan’ not in list1
True
>>> ‘Green’ not in list1
False

4.2.4 Slicing

Slicing operations allow us to create new list by taking out elements from an existing list.

>>> list1 =[‘Red’,‘Green’,‘Blue’,‘Cyan’,
‘Magenta’,‘Yellow’,‘Black’]
#subject from indexes 2 to 5 of list 1
>>> list1[2:6]
[‘Blue’, ‘Cyan’, ‘Magenta’, ‘Yellow’]

#list1 is truncated to the end of the list
>>> list1[2:20] #second index is out of range
[‘Blue’, ‘Cyan’, ‘Magenta’, ‘Yellow’,‘Black’]

>>> list1[7:2] $\qquad \qquad \qquad $ #first index > second index
[] $\qquad \qquad \qquad $ #results in an empty list

#return sublist from index 0 to 4
>>> list1[:5] $\qquad \qquad $ #first index missing
[‘Red’,‘Green’,‘Blue’,‘Cyan’,‘Magenta’]

#slicing with a given step size
>>> list1[0:6:2]
[‘Red’,‘Blue’,‘Magenta’]
#negative indexes
#elements at index -6,-5,-4,-3 are sliced
>>> list1[-6:-2]
[‘Green’,‘Blue’,‘Cyan’,‘Magenta’]

#both first and last index missing
>>> list1[::2] #step size 2 on entire list
[‘Red’,‘Blue’,‘Magenta’,‘Black’]

#Access list in the reverse order using
negative step size
>>> list1[::-1]
[‘Black’,‘Yellow’,‘Magenta’,‘Cyan’,‘Blue’, ‘Green’,‘Red’]

4.3 Traversing a List

We can access each element of the list or traverse a list using a for loop or a while loop.

(A) List traversal using for loop:

>>> list1 = [‘Red’,‘Green’,‘Blue’,‘Yellow’, ‘Black’]
>>> for item in list1:
print(item)

Output: print(item)

Red

Green

Blue

Yellow

Black

Another way of accessing the elements of the list is using range() and len() functions:

>>> for i in range(len(list1)):
print(list1[i])

Output:

Red

Green

Blue

Yellow

Black

len (list1) returns the length or total number of elements of list1. range(n) returns a sequence of numbers starting from 0 , increases by 1 and ends at n-1 (one number less than the specified number i.e. is)

4.4 List Methods and Built-in Functions

The data type list has several built-in methods that are useful in programming. Some of them are listed in Table 4.1.

Table 4.1 Built-in functions for list manipulation

4.5 List Manipulation

In this chapter, we have learnt to create a list and the different ways to manipulate lists. In the following programs, we will apply the various list manipulation methods.

Program 4-1 Write a program to allow user to perform any those list operation given in a menu. The menu is:

1. Append an element

2. Insert an element

3. Append a list to the given list

4. Modify an existing element

5. Delete an existing element from its position

6. Delete an existing element with a given value

7. Sort the list in the ascending order

8. Sort the list in descending order

9. Display the list.

#Program 4-1
#Menu driven program to do various list operations
myList $=[22,4,16,38,13]$ #myList having 5 elements
choice $=0$
For attempt in range (3): print (“Attempt number:”, attempt)
print(“The list ‘myList’ has the following elements”, myList)
print("\nL I S T OPERATIONS")
print(" 1. Append an element")
print(" 2. Insert an element at the desired position")
print(" 3 . Append a list to the given list")
print(" 4. Modify an existing element")
print(" 5 . Delete an existing element by its position")
print(" 6. Delete an existing element by its value")
print(" 7. Sort the list in ascending order")
print(" 8. Sort the list in descending order")
print(" 9. Display the list")
choice = int(input(“ENTER YOUR CHOICE (1-9): “))

#append element
if choice == 1:
element = eval(input(“Enter the element to be appended: “))
myList.append(element)
print(“The element has been appended\n”)

#insert an element at desired position
elif choice == 2:
element = eval(input(“Enter the element to be inserted: “))
pos = int(input(“Enter the position:”))
myList.insert(pos,element)
print(“The element has been inserted\n”)

#append a list to the given list
elif choice == 3:
newList = eval(input(“Enter the list to be appended: “))
myList.extend(newList)
print(“The list has been appended\n”)

#modify an existing element
elif choice == 4:
i = int(input(“Enter the position of the element to be modified: “))
if i < len(myList):
newElement = eval(input(“Enter the new element: “))
oldElement = myList[i]
myList[i] = newElement
print(“The element”,oldElement,“has been modified\n”)
else:
print(“Position of the element is more then the length of list”)

#delete an existing element by position
elif choice == 5:
i = int(input(“Enter the position of the element to be deleted: “))
if i < len(myList):
element = myList.pop(i)
print(“The element”,element,“has been deleted\n”)
else:
print("\nPosition of the element is more then the length of list”)

#delete an existing element by value
elif choice == 6:
element = int(input("\nEnter the element to be deleted: “))
if element in myList:
myList.remove(element)
print("\nThe element”,element,“has been deleted\n”)
else:
print("\nElement”,element,“is not present in the list”)

#list in sorted order
elif choice == 7:
myList.sort()
print("\nThe list has been sorted”)

#list in reverse sorted order
elif choice == 8:
myList.sort(reverse = True)
print("\nThe list has been sorted in reverse order”)

#display the list

#display the list
elif choice == 9:
print("\nThe list is:”, myList)
else:
print(“Choice is not valid”)

Output:

The list ‘myList’ has the following elements $[22,4,16,38,13]$ Attempt number : 1

L I S T 0 P E R A T I O N S

1. Append an element

2. Insert an element at the desired position

3. Append a list to the given list

4. Modify an existing element

5. Delete an existing element by its position

6. Delete an existing element by its value

7. Sort the list in ascending order

8. Sort the list in descending order

9. Display the list

ENTER YOUR CHOICE (1-10): 8

The list has been sorted in reverse order

The list ‘myList’ has the following elements $[38,22,16,13,4]$

Attempt number : 2

L I S T O P E R A T I O N S

1. Append an element

2. Insert an element at the desired position

3. Append a list to the given list

4. Modify an existing element

5. Delete an existing element by its position

6. Delete an existing element by its value

7. Sort the list in ascending order

8. Sort the list in descending order

9. Display the list

ENTER YOUR CHOICE (1-9) 5

Enter the position of the element to be deleted: 2

The element 16 has been deleted

The list ‘myList’ has the following elements $[38,22,13,4]$

Attempt number : 3

L I S T O P E R A T I O N S

1. Append an element

2. Insert an element at the desired position

3. Append a list to the given list

4. Modify an existing element

5. Delete an existing element by its position

6. Delete an existing element by its value

7. Sort the list in ascending order

8. Sort the list in descending order

9. Display the list

ENTER YOUR CHOICE (1-9) 10

choice is not valid

Program 4-2 A program to calculate average marks of $\mathrm{n}$ students where $\mathrm{n}$ is entered by the user.

#Program 4-2
#create an empty list
list1 = []
print(“How many students marks you want to enter: “)
n = int(input())
for i in range(0,n):
print(“Enter marks of student”,(i+1),”:”)
marks = int(input())
#append marks in the list
list1.append(marks)
#initialize total
total = 0
for marks in list1:

#add marks to total
total = total + marks
average = total / n
print(“Average marks of”,n,“students is:",average)

Output:

How many students marks you want to enter:

5

Enter marks of student 1:

45

Enter marks of student 2:

89

Enter marks of student 3:

79

Enter marks of student 4:

76

Enter marks of student 5:

55

Average marks of 5 students is: 68.8

Program 4-3 Write a program to check if a number is present in the list or not. If the number is present, print the position of the number. Print an appropriate message if the number is not present in the list.

#Program 4-3
list1 = [] $\qquad \qquad\qquad$ #Create an empty list
print(“How many numbers do you want to enter in the list: “)
maximum = int(input())
print(“Enter a list of numbers: “)
for i in range(0,maximum):
n = int(input())
list1.append(n) $\qquad \qquad\qquad$ #append numbers to the list
num = int(input(“Enter the number to be searched: “))

position = -1
for i in range (0, lin (list1)
if list1[i] == num: $\qquad \qquad\qquad$ #number is present
position = i+1 #save the position of number
if position == -1 :
print(“Number”,num,“is not present in the list”)
else:
print(“Number”,num,“is present at”,position + 1, “position”)

Output:

How many numbers do you want to enter in the list

5

Enter a list of numbers:

23

567

12

89

324

Enter the number to be searched:12

Number 12 is present at 3 position

4.6 Introduction to Dictionaries

The data type dictionary falls under mapping. It is a mapping between a set of keys and a set of values. The key-value pair is called an item. A key is separated from its value by a colon(:) and consecutive items are separated by commas. Items in dictionaries are unordered, so we may not get back the data in the same order in which we had entered the data initially in the dictionary.

4.6.1 Creating a Dictionary

To create a dictionary, the items entered are separated by commas and enclosed in curly braces. Each item is a key value pair, separated through colon (:). The keys in the dictionary must be unique and should be of any immutable data type i.e. number, string or tuple. The values can be repeated and can be of any data type.

Example 4.2

#dict1 is an empty dictionary
>>> dict1 = {}
>>> dict1
{}
#dict3 is the dictionary that maps names of
#the students to marks in percentage
>>> dict3 = {‘Mohan’:95,‘Ram’:89,‘Suhel’:92,
‘Sangeeta’:85}
>>> dict3
{‘Mohan’: 95, ‘Ram’: 89, ‘Suhel’: 92,
‘Sangeeta’: 85}

4.6.2 Accessing Items in a Dictionary

We have already seen that the items of a sequence (string, list and tuple) are accessed using a technique called indexing. The items of a dictionary are accessed via the keys rather than via their relative positions or indices. Each key serves as the index and maps to a value.

The following example shows how a dictionary returns the value corresponding to the given key:

>>> dict3 = {‘Mohan’:95,‘Ram’:89,‘Suhel’:92,
‘Sangeeta’:85}
>>> dict3[‘Ram’]
89
>>> dict3[‘Sangeeta’]
85
#using unspecified key
>>> dict3[‘Shyam’]
KeyError: ‘Shyam’

In the above examples the key ‘Ram’ always maps to the value 89 and key ‘Sangeeta’ always maps to the value 85. So the order of items does not matter. If the key is not present in the dictionary we get KeyError.

4.6.3 Membership Operation

The membership operator in checks if the key is present in the dictionary and returns True, else it returns False.

>>> dict1 = {‘Mohan’:95,‘Ram’:89,‘Suhel’:92,
‘Sangeeta’:85}
>>> ‘Suhel’ in dict1
True

The not in operator returns True if the key is not present in the dictionary, else it returns False.

>>> dict1 = {‘Mohan’:95,‘Ram’:89,‘Suhel’:92,
‘Sangeeta’:85}
>>> ‘Suhel’ not in dict1
False

4.6.4 Dictionaries are Mutable

Dictionaries are mutable which implies that the contents of the dictionary can be changed after it has been created.

(A) Adding a new item

We can add a new item to the dictionary as shown in the following example:

>>> dict1 = {‘Mohan’:95,‘Ram’:89,‘Suhel’:92,
‘Sangeeta’:85}
>>> dict1[‘Meena’] = 78
>>> dict1
{‘Mohan’: 95, ‘Ram’: 89, ‘Suhel’: 92,
‘Sangeeta’: 85, ‘Meena’: 78}

(B) Modifying an existing item

The existing dictionary can be modified by just overwriting the key-value pair. Example to modify a given item in the dictionary:

>>> dict1 = {‘Mohan’:95,‘Ram’:89,‘Suhel’:92,
‘Sangeeta’:85}
#Marks of Suhel changed to 93.5
>>> dict1[‘Suhel’] = 93.5
>>> dict1
{‘Mohan’: 95, ‘Ram’: 89, ‘Suhel’: 93.5,
‘Sangeeta’: 85}

4.7 Traversing a Dictionary

We can access each item of the dictionary or traverse a dictionary using for loop.

>>> dict1 = {‘Mohan’:95,‘Ram’:89,‘Suhel’:92,
‘Sangeeta’:85}

Method 1:

>>> for key in dict1:
$\qquad$ print(key, ‘:’ ,dict1[key])
Mohan: 95
Ram: 89
Suhel: 92
Sangeeta: 85

Method 2:

>>> for key,value in dict1.items():
$\qquad$ print(key,’:’,value)
Mohan: 95
Ram: 89
Suhel: 92
Sangeeta: 85

4.8 Dictionary Methods and Built-in Functions

Python provides many functions to work on dictionaries. Table 4.2 lists some of the commonly used dictionary methods.

Table 4.2 Built-in functions and methods for dictionary

4.9 Manipulating Dictionaries

In this chapter, we have learnt how to create a dictionary and apply various methods to manipulate it. The following examples show the application of those manipulation methods on dictionaries.

(a) Create a dictionary ‘ODD’ of odd numbers between 1 and 10 , where the key is the decimal number and the value is the corresponding number in words.

>>> ODD = {1:‘One’,3:‘Three’,5:‘Five’,7:‘Seven’,9:‘Nine’}
>>> ODD
{1: ‘One’, 3: ‘Three’, 5: ‘Five’, 7: ‘Seven’, 9: ‘Nine’}

(b) Display the keys in dictionary ‘ODD’.

>>> ODD.keys()
dict_keys([1, 3, 5, 7, 9])

(c) Display the values in dictionary ‘ODD’.

>>> ODD.values ( )
dict_values([‘One’, ‘Three’, ‘Five’, ‘Seven’, ‘Nine’])

(d) Display the items from dictionary ‘ODD’

>>> ODD.items()
dict_items([(1, ‘One’), (3, ‘Three’), (5, ‘Five’), (7, ‘Seven’), (9, ‘Nine’)])

(e) Find the length of the dictionary ‘ODD’.

>>> len(ODD)
5

(f) Check if 7 is present or not in dictionary ‘ODD’

>>> 7 in ODD
True

(g) Check if 2 is present or not in dictionary ‘ODD’ » 2 in ODD

>>> 2 in ODD
False

(h) Retrieve the value corresponding to the key 9

>>> ODD.get(9)
‘Nine’

(i) Delete the item from the dictionary, corresponding to the key 9. ‘ODD’

>>> del ODD[9]
>>> ODD
{1: ‘One’, 3: ‘Three’, 5: ‘Five’, 7: ‘Seven’}

Program 4-4 $\sigma$ n number of write a program to enter names of employees and their salaries as input and store them in a dictionary. Here $\mathrm{n}$ is to input by the user.

#Program 4-4
#Program to create a dictionary which stores names of employees
#and their salary
num = int(input(“Enter the number of employees whose data to be stored: “))
count = 1
employee = dict() $\qquad \qquad \qquad$ #create an empty dictionary
for count in range (n):
$\qquad$ name = input(“Enter the name of the Employee: “)
$\qquad$ salary = int(input(“Enter the salary: “))
$\qquad$ employee[name] = salary
print("\n\nEMPLOYEE_NAME\tSALARY”)
for k in employee:
$\qquad$ print(k,’\t\t’,employee[k])

Output:

Enter the number of employees to be stored: 5

Enter the name of the Employee: ‘Tarun’

Enter the salary: 12000

Enter the name of the Employee: ‘Amina’

Enter the salary: 34000

Enter the name of the Employee: ‘Joseph’

Enter the salary: 24000

Enter the name of the Employee: ‘Rahul’

Enter the salary: 30000

Enter the name of the Employee: ‘Zoya’

Enter the salary: 25000

EMPLOYEE_NAME SALARY

‘Tarun’ $\qquad$ 12000

‘Amina’ $\qquad$ 34000

‘Joseph’ $\qquad$ 24000

‘Rahul’ $\qquad$ 30000

‘Zoya’$\qquad$ 25000

Program 4-5 Write a program to count the number of times a character appears in a given string.

#Program 4-5
#Count the number of times a character appears in a given string
st = input(“Enter a string: “)
dic = { } $\qquad \qquad \qquad$ #creates an empty dictionary
for ch in st:
$\qquad $ if ch in dic: $\qquad \qquad \qquad$ #if next character is already in dic
$\qquad \qquad$ dic[ch] += 1
$\qquad $ else:
$\qquad $ $\qquad $ dic[ch] = 1 $\qquad \qquad \qquad$ #if ch appears for the first time

for key in dic:
$\qquad$ print(key,’:’,dic[key])

Output:

Enter a string: Helloworld

H : 1

e : 1

l : 3

o : 2

W : 1

r : 1

d : 1

Program 4-6 Write a program to convert a number entered by the user into its corresponding number in words. for example if the input is 876 then the output should be ‘Eight Seven Six’.

#Program 4-6
num = input(“Enter any number: “) #number is stored as string
$\quad$ #numberNames is a dictionary of digits and corresponding number
$\quad$ #names
$\quad$ numberNames = {0:‘Zero’,1:‘One’,2:‘Two’,3:‘Three’,4:‘Four’,\
$\quad\quad\quad$$\quad$$\quad$$\quad$$\quad$ 5:‘Five’,6:‘Six’,7:‘Seven’,8:‘Eight’,9:‘Nine’}

result = ‘’
for ch in num:
$\quad$ key = int(ch) $\quad \quad$ #converts character to integer
$\quad$ value = numberNames[key]

$\quad$ $\quad$ result = result + ’ ’ + value
print(“The number is:",num)
print(“The numberName is:",result)

Output:

Enter any number: 6512

The number is: 6512

The numberName is: Six Five One Two

Summary

• Lists are mutable sequences in Python, i.e. we can change the elements of the list.
• Elements of a list are put in square brackets separated by comma.
• List indexing is same as that of list and starts at 0 . Two way indexing allows traversing the list in the forward as well as in the backward direction.
• Operator + concatenates one list to the end of other list.
• Operator * repeats the content of a list by specified number of times.
• Membership operator in tells if an element is present in the list or not and not in does the opposite.
• Slicing is used to extract a part of the list.
• There are many list manipulation methods. Few are: len(), list(), append(), extend(), insert(), count(), find(), remove(), pop(), reverse(), sort(), sorted(), $\min (), \max (), \operatorname{sum}()$.
• Dictionary is a mapping (non scalar) data type. It is an unordered collection of key-value pair; keyvalue pair are put inside curly braces.
• Each key is separated from its value by a colon.
• Keys are unique and act as the index.
• Keys are of immutable type but values can be mutable.

Exercise

1. What will be the output of the following statements?

a) list1 = [12,32,65,26,80,10]
$\quad$ list1.sort()
$\quad$ print(list1)

b) list1 = [12,32,65,26,80,10]
$\quad$ sorted(list1)
$\quad$ print(list1)

c) list1 = [1,2,3,4,5,6,7,8,9,10]
$\quad$ list1[::-2]
$\quad$ list1[:3] + list1[3:]

d) list1 = [1,2,3,4,5]
$\quad$ list1[len(list1)-1]

2. Consider the following list myList. What will be the elements of myList after each of the following operations?

myList =[10,20,30,40]

a) myList.append ([50,60])

b) myList.extend( [80,90])

3. What will be the output of the following code segment?

myList = [1,2,3,4,5,6,7,8,9,10]
for i in range(0,len(myList)):
$\quad$if i%2 == 0:
$\quad\quad$ print(myList[i])

4. What will be the output of the following code segment?

a) myList = [1,2,3,4,5,6,7,8,9,10]
$\quad$ del myList[3:]
$\quad$ print(myList)

b) myList = [1,2,3,4,5,6,7,8,9,10]
$\quad$ del myList[:5]
$\quad$ print(myList)

c) myList = [1,2,3,4,5,6,7,8,9,10]
$\quad$ del myList[::2]
$\quad$ print(myList)

del myList[::2] print (myList)

5. Differentiate between append() and extend() methods of list.

6. Consider a list:

list1 = [6,7,8,9]

What is the difference between the following operations on list1:

a) list1 * 2

b) list1 *=2

c) list1 = list 1 * 2

7. The record of a student (Name, Roll No, Marks in five subjects and percentage of marks) is stored in the following list:

stRecord = [’ ‘Raman’ ,‘A-36’, [56,98,99,72,69], 78.8]

Write Python statements to retrieve the following information from the list stRecord.

a) Percentage of the student

b) Marks in the fifth subject

c) Maximum marks of the student

d) Roll No. of the student

e) Change the name of the student from ‘Raman’ to ‘Raghav’

8. Consider the following dictionary stateCapital:

stateCapital = {“Assam”:“Guwahati”, “Bihar”:“Patna”,“Maharashtra”:“Mumbai”, “Rajasthan”:“Jaipur”}

Find the output of the following statements:

a) print(stateCapital.get(“Bihar”))

b) print (statecapital.keys())

c) print (statecapital.values())

d) print(statecapital.items())

e) print(len(stateCapital))

f) print(“Maharashtra” in stateCapital)

g) print(stateCapital.get(“Assam”))

h) del stateCapital[“Assam”] print(stateCapital)

Programming Problems

1. Write a program to find the number of times an element occurs in the list.

2. Write a program to read a list of $n$ integers (positive as well as negative). Create two new lists, one having all positive numbers and the other having all negative numbers from the given list. Print all three lists.

3. Write a program to find the largest and the second largest elements in a given list of elements.

4. Write a program to read a list of $n$ integers and find their median.

Note: The median value of a list of values is the middle one when they are arranged in order. If there are two middle values then take their average.

Hint: Use an inbuilt function to sort the list.

5. Write a program to read a list of elements. Modify this list so that it does not contain any duplicate elements i.e. all elements occurring multiple times in the list should appear only once.

6. Write a program to create a list of elements. Input an element from the user that has to be inserted in the list. Also input the position at which it is to be inserted.

7. Write a program to read elements of a list and do the following.

a) The program should ask for the position of the element to be deleted from the list and delete the element at the desired position in the list.

b) The program should ask for the value of the element to be deleted from the list and delete this value from the list.

8. Write a Python program to find the highest 2 values in a dictionary.

9. Write a Python program to create a dictionary from a string ‘w3resource’ such that each individual character mates a key and its index value for fist occurrence males the corresponding value in dictionary.

Expected output: {3 ‘: 1, ’s’: 4, ‘r’: 2, ‘u’: 6, ‘w’: 0, ‘c’: 8, ’e’: 3, ‘o’: 5 }

10. Write a program to input your friend’s, names and their phone numbers and store them in the dictionary as the key-value pair. Perform the following operations on the dictionary:

a) Display the Name and Phone number for all your friends.

b) Add a new key-value pair in this dictionary and display the modified dictionary c) Delete a particular friend from the dictionary

d) Modify the phone number of an existing friend

e) Check if a friend is present in the dictionary or not

f) Display the dictionary in sorted order of names

Case Study Based Question

For the SMIS System given in Chapter 3, let us do the following:

1. Write a program to take in the roll number, name and percentage of marks for $\mathrm{n}$ students of Class $\mathrm{X}$ and do the following:

• Accept details of the $\mathrm{n}$ students ( $\mathrm{n}$ is the number of students).
• Search details of a particular student on the basis of roll number and display result.
• Display the result of all the students.
• Find the topper amongst them.
• Find the subject toppers amongst them.

(Hint: Use Dictionary, where the key can be roll number and the value an immutable data type containing name and percentage.)

Case Study

1. A bank is a financial institution which is involved in borrowing and lending of money. With advancement in technology, online banking, also known as internet banking allows customers of a bank to conduct a range of financial transactions through the bank’s website anytime, anywhere. As part of initial investigation you are suggested to:

• Collect a Bank’s application form. After careful analysis of the form, identify the information required for opening a savings account. Also enquire about the rate of interest offered for a savings account.
• The basic two operations performed on an account are Deposit and Withdrawal. Write a menu driven program that accepts either of the two choices of Deposit and Withdrawal, then accepts an amount, performs the transaction and accordingly displays the balance. Remember every bank has a requirement of minimum balance which needs to be taken care of during withdrawal operations.

Enquire about the minimum balance required in your bank.

• Collect the interest rates for opening a fixed deposit in various slabs in a savings bank account. Remembers rate may be different for senior citizens.

Finally, write a menu driven program having the following options (use functions and appropriate data types):

• Open a savings bank account
• Deposit money
• Withdraw money
• Take details such as amount and period for a Fixed Deposit and display its maturity amount for a particular customer.

2. Participating in a quiz can be fun as it provides a competitive element. Some educational institutes use it as a tool to measure knowledge level, abilities and/ or skills of their pupils either on a general level or in a specific field of study. Identify and analyse popular quiz shows and write a Python program to create a quiz that should also contain the following functionalities besides the one identified by you as a result of your analysis.

• Create an administrative user ID and password to categorically add or modify delete a question.
• Register the student before allowing her/him to play a quiz.
• Allow selection of category based on subject area.
• Display questions as per the chosen category.
• Keep the score as the participant plays.
• Display final score.

3. Our heritage monuments are our assets. They are a reflection of our rich and glorious past and an inspiration for our future. UNESCO has identified some of Indian heritage sites as World Heritage sites. Collect the following information about these sites:

• What is the name of the site?
• Where is it located?
• District
• State
• When was it built?
• Who built it?
• Why was it built?
• Website link (if any)

Write a Python program to:

• Create an administrative user ID and password to add, modify or delete an entered heritage site in the list of sites.
• Display the list of world heritage sites in India.
• Search and display information of a world heritage site entered by the user.
• Display the name(s) of world heritage site(s) on the basis of the state input by the user.