Sets in Pyhton

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_B
print(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.

Qus Start with the list[8,9,10]. Do the following using list functions

(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.


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


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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


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


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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


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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


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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.


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


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Write a program to swap two values using tuple assignment


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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


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


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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.


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


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WAP to calculate mean of a given list of numbers.


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


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


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WAP to calculate the sum of integers of the list


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WAP that reverses an array of integers (in place)


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WAP that creates a third list after adding two lists.


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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.


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


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