# O Level Exam

#### Sets in Pyhton

In python, a set is another type of collection data type. A Set is a mutable and an unordered collection of elements without duplicates. That means the elements within a set cannot be repeated. This feature used to include membership testing and eliminating duplicate elements.

Creating a Set

A set is created by placing all the elements separated by comma within a pair of curly brackets. The set( ) function can also used to create sets in Python.

Syntax:

`Set_Variable = {E1, E2, E3 …….. En}`

Example

`>>> S1={1,2,3,'A',3.14}>>> print(S1){1, 2, 3, 3.14, 'A'}>>> S2={1,2,2,'A',3.14}>>> print(S2){1, 2, 'A', 3.14}`

In the above examples, the set S1 is created with different types of elements without duplicate values. Whereas in the set S2 is created with duplicate values, but python accepts only one element among the duplications. Which means python removed the duplicate value, because a set in python cannot have duplicate elements.

Creating Set using List or Tuple

A list or Tuple can be converted as set by using set( ) function. This is very simple procedure. First you have to create a list or Tuple then, substitute its variable within set( ) function as argument.

Example

`MyList=[2,4,6,8,10]MySet=set(MyList)print(MySet)`

Output:

{2, 4, 6, 8, 10}

Set Operations

As you learnt in mathematics, the python is also supports the set operations such as Union, Intersection, difference and Symmetric difference.

Union: It includes all elements from two or more sets

Positive Numbers: (5, 6, 8, 3, 1)

In python, the operator | is used to union of two sets. The function union( ) is also used to join two sets in python.

Example: Program to Join (Union) two sets using union operator

`set_A={2,4,6,8}set_B={'A', 'B', 'C', 'D'}U_set=set_A|set_Bprint(U_set)`

Output:

{2, 4, 6, 8, 'A', 'D', 'C', 'B'}

Example: Program to Join (Union) two sets using union function

`set_A={2,4,6,8}set_B={'A', 'B', 'C', 'D'}set_U=set_A.print(set_U)`

Output:

{'D', 2, 4, 6, 8, 'B', 'C', 'A'}

(ii) Intersection: It includes the common elements in two sets

Th e operator & is used to intersect two sets in python. Th e function intersection( ) is also used to intersect two sets in python.

Example: Program to insect two sets using intersection operator

`set_A={'A', 2, 4, 'D'}set_B={'A', 'B', 'C', 'D'}print(set_A & set_B)`

Output:

{'A', 'D'}

Example: Program to insect two sets using intersection function

set_A={'A', 2, 4, 'D'}

set_B={'A', 'B', 'C', 'D'}

print(set_A.intersection(set_B))

Output:

{'A', 'D'}

(iii) DifferenceIt includes all elements that are in fi rst set (say set A) but not in the second set (say set B)

Th e minus (-) operator is used to diff erence set operation in python. Th e function difference( ) is also used to diff erence operation.

Example: Program to difference of two sets using minus operator

`set_A={'A', 2, 4, 'D'}set_B={'A', 'B', 'C', 'D'}print(set_A - set_B)`

Output:

{2, 4}

Example: Program to difference of two sets using difference function

`set_A={'A', 2, 4, 'D'}set_B={'A', 'B', 'C', 'D'}print(set_A.diff erence(set_B))`

Output:

{2, 4}

(iv) Symmetric difference : It includes all the elements that are in two sets (say sets A and B) but not the one that are common to two sets.

The caret (^) operator is used to symmetric difference set operation in python. The function symmetric_difference( ) is also used to do the same operation.

Example: Program to symmetric difference of two sets using caret operator

`set_A={'A', 2, 4, 'D'}set_B={'A', 'B', 'C', 'D'}print(set_A ^ set_B)`

Output:

{2, 4, 'B', 'C'}

Example: Program to difference of two sets using symmetric difference function

`set_A={'A', 2, 4, 'D'}set_B={'A', 'B', 'C', 'D'}print(set_A.symmetric_difference(set_B))`

Output:

{2, 4, 'B', 'C'}

Qus What do you understand by mutability?

Ans: Mutable means changeable. In Python, mutable types are those whose values can be changed in place. Only three types are mutable in python – Lists, Dictionaries and Sets.

(a) Set the second entry (index 1) to 17

(b) Add 4, 5 and 6 to the end of the list.

(c) Remove the first entry from the list.

(d) Sort the list.

(e) Double the list.

(f) Insert 25 at index 3

Ans:

(a) list[1]=17

(b) list.append(4)

list.append(5)

list.append(6)

(c) list.pop(0)

(d) list.sort()

(e) list=list*2

(f) list.insert(3,25)

Qus.  If a is [1, 2, 3], what is the difference (if any) between a*3 and [a, a, a]?

Ans: a*3 will produce [1,2,3,1,2,3,1,2,3], means a list of integers and [a, a, a] will produce [[1,2,3],[1,2,3],[1,2,3]], means list of lists

Qus. If a is [1, 2, 3], is a *3 equivalent to a + a + a?

Ans: Yes, Both a*3 and a+a+a will produce same result.

Qus. If a is [1, 2, 3], what is the meaning of a [1:1] = 9?

Ans: This will generate an error "TypeError: can only assign an iterable'.

Qus If a is [1, 2, 3], what is the meaning of a [1:2] = 4 and a [1:1] = 4?

Ans: These will generate an error "TypeError: can only assign an iterable".

Qus. What are list slices?

Ans: List slices are the sub-part of a list extracted out. You can use indexes of the list elements to create list slices as per following format. Syntax is as follows –

Qus Does a slice operator always produce a new list?

Ans: Yes, this will create a new list.

Qus. How are lists different from strings when both are sequences?

Ans: Lists are similar to strings in many ways like indexing, slicing, and accessing individual elements but they are different in the sense that

(i) Lists are mutable while strings are immutable.

(ii) In consecutive locations, strings store the individual characters while list stores the references of its elements.

(iii) Strings store single type of elements-all characters while lists can store elements belonging to different types.

Qus. What are nested Lists?

Ans: A list can have an element in it, which itself is a list. Such a list is called nested list. e.g.

L = [1,2,3,4,[5,6,7],8]

Qus. Discuss the utility and significance of Lists.

Ans: The list is a most versatile datatype available in Python which can be written as a list of comma-separated values (items) between square brackets. Important thing about a list is that items in a list need not be of the same type. List is majorly used with dictionaries when there is large number of data.

Qus What is the purpose of the del operator and pop method? Try deleting a slice.

Ans: del operator is used to remove an individual item, or to remove all items identified by a slice. It is to be used as per syntax given below –

>>>del List[index]

>>>del List[start:stop]

pop method is used to remove single element, not list slices. The pop() method removes an individual item and returns it. Its syntax is –

>>>a=List.pop() #this will remove last item and deleted item will be assigned to a.

>>>a=List[10] # this will remove the ite at index 10 and deleted item will be assigned to a.

Qus. What are list slices?

Ans: List slices, like string slices are the sub part of a list extracted out. Indexes can be used to create list slices as per following format:

seq = L[start:stop]

Qus. What do you understand by true copy of a list? How is it different from shallow copy?

Ans: A shallow copy means constructing a new collection object and then populating it with references to the child objects found in the original. In essence, a shallow copy is only one level deep. The copying process does not recurse and therefore won‘t create copies of the child objects themselves.

True Copy means you can create a copy of a list using New_list=My_list. The assignment just copies the reference to the list, not the actual list, so both new_list and my_list refer to the same list after the assignment.

Qus What do you understand by immutability?

Ans: Immutability means not changeable. The immutable types are those that can never change their value in place. In python following types are immutable –

I. Integers

II. Floating point numbers

III. Booleans

IV. Strings

V. Tuples

Qus How are Tuples different from Lists when both are sequences?

Ans: Tuples are similar to lists in many ways like indexing, slicing, and accessing individual values but they are different in the sense that –

Tuples are immutable while lists are mutable.

List can grow or shrink while tuples cannot.

Qus Can tuples be nested?

Ans: Yes, tuples can be nested. e.g (1,2,3,(4,5,6))

Qus. Discuss the utility and significance of Tuples.

Ans: Tuples are great for holding static data that you don't plan on modifying and changing a lot. Tuples are four to seven times faster than lists. This means for every list item manipulated, four to seven tuples could be manipulated within that time frame. This has huge advantages for scientific work, as this allows for speedy data reading.

Qus. How can you say that a tuple is an ordered list of objects?

Ans: A tuple is an ordered list of objects. This is evidenced by the fact that the objects can be accessed through the use of an ordinal index amd for a given index, same element is returned every time.

Qus. Why can‟t List can be used as keys?

Ans: List is mutable datatype. And Keys of dictionary must be immutable type. This is the region that list cannot be used as keys.

Qus. What type of objects can be used as keys in dictionary?

Ans: Any immutable objects can be used as keys in dictionary.

Qus. Can you change the order of the dictionaries contents?

Ans: Yes, the order of dictionary contents may be changed.

Qus. Can you modify the keys in a dictionary?

Ans: Keys cannot be modified in dictionary while values are mutable in dictionary.

Qus. Can you modify the value in a dictionary?

Ans: Yes, Values can be modified in dictionaries.

Qus. Is dictionary Mutable? Why?

Ans: Dictionary is mutable type because we can change its values.

Qus How are dictionaries different from Lists?

Ans: The dictionary is similar to lists in the sense that it is also a collection of data-items but it is different from lists in the sense that lists are sequential collections(ordered) and dictionaries are non-sequential collections(unordered).

Elements in lists or tuples can be accessed by using indexes. But in dictionaries the values can be obtained using keys. By changing the sequence of key we can shuffle the order of elements of dictionary while this thing is not possible in list.

Qus. When are dictionaries more useful than lists?

Ans: Dictionaries can be much more useful than lists when we wanted to store all our friends cell-phone numbers. We could create a list of pairs,(name of friend, phone number), but once this list becomes long enough searching this list for a specific phone number will get-time consuming. Better would be if we could index the list by our friend‘s name. This is precisely what a dictionary does.

Qus. Discuss the utility and significance of Dictionaries.

Ans: Dictionaries can be much more useful than lists when we wanted to store all our friends cell-phone numbers. We could create a list of pairs,(name of friend, phone number), but once this list becomes long enough searching this list for a specific phone number will get-time consuming. Better would be if we could index the list by our friend‘s name. This is precisely what a dictionary does.

Qus. Why is a dictionary termed as an unordered collection of objects?

Ans: But in dictionaries the values can be obtained using keys. By changing the sequence of key we can shuffle the order of elements of dictionary while this thing is not possible in list. In dictionaries there is no index. It uses its keys as index which can be rearranged. That‘s why a dictionary termed as an unordered collection of objects

Qus. How is clear() function different from del <dict> Statement?

Ans: clear() removes all the elements of a dictionary and makes it empty dictionary while del statement removes the complete dictionary as an object. After del statement with a dictionary name, that dictionary object no longer exists, not even empty dictionary.

#### Programs

WAP to find the 2nd largest number from the list of the numbers entered through keyboard.

Write a python program that creates a list of numbers from 1 to 20 that are divisible by 4

Write a python program to define a list of countries that are a member of BRICS. Check whether a county is member of BRICS or not

Python program to read marks of six subjects and to print the marks scored in each subject and show the total marks

Python program to read prices of 5 items in a list and then display sum of all the prices, product of all the prices and find the average

Python program to count the number of employees earning more than 1 lakh per annum. The monthly salaries of n number of employees are given

Write a program to create a list of numbers in the range 1 to 10. Then delete all the even numbers from the list and print the final list.

Write a program to generate in the Fibonacci series and store it in a list. Then find the sum of all values.

Write a program to swap two values using tuple assignment

Write a python program using a function that returns the area and circumference of a circle whose radius is passed as an argument.two values using tuple assignment

Write a program that has a list of positive and negative numbers. Create a new tuple that has only positive numbers from the list

Python Program that generate a set of prime numbers and another set of even numbers. Demonstrate the result of union, intersection, difference and symmetirc difference operations.

WAP to find minimum element from a list of elements along with its index in the list.

WAP to calculate mean of a given list of numbers.

WAP to search for an element in a given list of numbers.

WAP to count frequency of a given element in a list of numbers.

WAP to calculate the sum of integers of the list

WAP that reverses an array of integers (in place)

WAP that creates a third list after adding two lists.

WAP that repeatedly asks the user to enter product names and prices. Store all of them in a dictionary whose keys are product names and values are prices. And also write a code to search an item from the dictionary.

WAP to create a dictionary named year whose keys are month names and values are their corresponding number of days.

write  a program that input a list, replace it twice and then prints the sorted list in ascending and descending order.

write a program to check if the maximum element of the list lies in the first half of the list or in the second half.

write a program to input two lists and display the maximum elements from the elements of both the list combined, along with its index in its list.

write a program to input a list of numbers and swap elements at the even location with the elements at the odd location.

Write a program rotates the elements of a list so that the elements at the first index moves to the second index , the element in the second index moves to the third index, etc., and the element at the last index moves to the first index.

Write a program to input ‘n’ numbers and store it in a tuple and find maximum & minimum values in the tuple.

Write a program to input any two tuples and interchange the tuple values.

Write a program to input any two tuples and interchange the tuple values.

Write a python program to increment the elements of a list with a number.

Ask the use to enter a list containing number between 1 and 12, then replace all the entries in the list that are  greater than 10 with 10

Write a Python program that reverse a list of integers (in place)

Write a python program that inputs two lists and creates a third, that contains all elements of the first followed by all elements of the second.

Ask the user to inter list of string. Create a new list that consist of those strings with their first characters removed.

Write a Python program to Create a list using for loop which consist of integers 0 through 49

Write a Python program to create a list using for loop which consist square of  the integers 1 through 50

Write a Python program to create a list using for loop which consist ['a','bb','ccc','dddd',....] that ends with 26 copies of the letter z.

Write a python program that takes any two list L and M of the same size and adds their elements together to from a new list N whose elements are sums of the corresponding elements in L and M. For instance, if L=[3,1,4] and M= [1,5,9] the N should equal [4,6,13].

Write a python program to rotates the elements of a list so that the elements at the first index moves to the second index, the element in the second index moves to the third index, etc. and the elements in the last index moves to the first index.

Write a python program to move all duplicate values in a list to the end of the list.

Write a Python program display the maximum and minimum values form specified range of indexes of a list

Write a python program to compare two equal sized list and print the first index where they differ

Write a Python program to enter names of employees and their salaries as input and store them in a dictionary

Write a program to count the number of times a character appears in a given string

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'.

Repeatedly ask the user to enter a team name and how many games the team has won and how many they lost. Store this information in a dictionary where the keys are the team names and the values are a list of the form [wins, losses ].

(i) using the dictionary created above, allow the user to enter a team name and print out the team’s winning percentage.

(ii) using dictionary create a list whose entries are the number of wins for each team.

(iii) using the dictionary, create a list of all those teams that have winning records.

Write a program that repeatedly asks the user to enter product names and prices. Store all of these  in a dictionary whose keys are the product names and whose values are the price .

When the user is done entering products and price, allow them to repeatedly enter a product name and print the corresponding price or a message if the product is not in dictionary.

Create a dictionary whose keys are month name and whose values are number of days in the corresponding month:

(a) ask the user to enter the month name and use the dictionary to tell how many days are in month .

(b) print out all of the keys in alphabetical order  .

(c) print out all of the month with 31 days.

(d) print out the (key - value) pair sorted  by the number of the days in each month .

Can you store the detail of 10 students in a dictionary at the same time? details include – rollno, name ,marks ,grade etc. Give example to support your answer.

Given the dictionary x = {‘k1’: ‘v1’, ‘k2’ : ‘v2’, ‘k3’ : ‘v3’} ,create a dictionary with the opposite mapping.

Write a program to create the dictionary .

Given two dictionaries say d1 and d2

Write a program that lists the over lapping keys of the two dictionaries if a key of d1 is also a key of d2 , the list it .

Write a program that checks if two same values in a dictionary have different keys.

Write a program to check if a dictionary is contained in another dictionary.

e.g., if

d1 = {1:11, 2:12}

d2 = {1:11, 2:12, 3:13, 4:15}

Then d1 is contained in d2.

A dictionary D1 has values in the form of lists of numbers. Write a program to create a new dictionary D2 having same keys as D1 but values as the sum of the list elements.

e.g.

D1 = {'A': [1, 2, 3], 'B': [4, 5, 6]}

Then

D2 is {'A':6, 'B': 15}

A dictionary has three keys: 'assets', 'liabilities' and 'capital'. Each of these keys store their value in form of a list storing various values of 'assets', liabilities' and 'capital' respectively. Write a program to create a dictionary in this form and print. Also test if the accounting equation holds true.