NIELIT O Level Exam : python

Tuple in Python

Tuples consists of a number of values separated by comma and enclosed within parentheses. Tuple is similar to list, values in a list can be changed but not in a tuple.

The term Tuple is originated from the Latin word represents an abstraction of the sequence of numbers:
single(1), double(2), triple(3), quadruple(4), quintuple(5), sextuple(6), septuple(7), octuple(8), ..., n‑tuple, ...,

Advantages of Tuples over list

1. The elements of a list are changeable (mutable) whereas the elements of a tuple are unchangeable (immutable), this is the key difference between tuples and list.

2. The elements of a list are enclosed within square brackets. But, the elements of a tuple are enclosed by paranthesis.

3. Iterating tuples is faster than list.

Creating Tuples

Creating tuples is similar to list. In a list, elements are defined within square brackets, whereas in tuples, they may be enclosed by parenthesis. The elements of a tuple can be even defined without parenthesis. Whether the elements defined within parenthesis or without parenthesis, there is no differente in it's function.

Syntax:

# Empty tuple
Tuple_Name = ( )
# Tuple with n number elements
Tuple_Name = (E1, E2, E2 ……. En)
# Elements of a tuple without parenthesis
Tuple_Name = E1, E2, E3 ….. En

Example

>>> MyTup1 = (23, 56, 89, 'A', 'E', 'I', "Tamil")
>>> print(MyTup1)
(23, 56, 89, 'A', 'E', 'I', 'Tamil')
>>> MyTup2 = 23, 56, 89, 'A', 'E', 'I', "Tamil"
>>> print (MyTup2)
(23, 56, 89, 'A', 'E', 'I', 'Tamil')

(i) Creating tuples using tuple( ) function

The tuple( ) function is used to create Tuples from a list. When you create a tuple, from a list, the elements should be enclosed within square brackets.

Syntax:

Tuple_Name = tuple( [list elements] )

Example

>>> MyTup3 = tuple( [23, 45, 90] )
>>> print(MyTup3)
(23, 45, 90)
>>> type (MyTup3)
<class ‘tuple’>

(ii) Creating Single element tuple

While creating a tuple with a single element, add a comma at the end of the element. In the absence of a comma, Python will consider the element as an ordinary data type; not a tuple. Creating a Tuple with one element is called “Singleton” tuple.

Example

>>> MyTup4 = (10)
>>> type(MyTup4)
<class 'int'>
>>> MyTup5 = (10,)
>>> type(MyTup5)
<class 'tuple'>

Accessing values in a Tuple

Like list, each element of tuple has an index number starting from zero. The elements of a tuple can be easily accessed by using index number.

Example

>>> Tup1 = (12, 78, 91, “Tamil”, “Telugu”, 3.14, 69.48)
# to access all the elements of a tuple
>>> print(Tup1)
(12, 78, 91, 'Tamil', 'Telugu', 3.14, 69.48)
#accessing selected elements using indices
>>> print(Tup1[2:5])
(91, 'Tamil', 'Telugu')
#accessing from the first element up to the specified index value
>>> print(Tup1[:5])
(12, 78, 91, 'Tamil', 'Telugu')
# accessing from the specified element up to the last element.
>>> print(Tup1[4:])
('Telugu', 3.14, 69.48)
# accessing from the first element to the last element
>>> print(Tup1[:])
(12, 78, 91, 'Tamil', 'Telugu', 3.14, 69.48)

Update and Delete Tuple

As you know a tuple is immutable, the elements in a tuple cannot be changed. Instead of altering values in a tuple, joining two tuples or deleting the entire tuple is possible.

Example

# Program to join two tuples
Tup1 = (2,4,6,8,10)
Tup2 = (1,3,5,7,9)
Tup3 = Tup1 + Tup2
print(Tup3)

Output

(2, 4, 6, 8, 10, 1, 3, 5, 7, 9)

To delete an entire tuple, the del command can be used.

Syntax:

del tuple_name

Example

Tup1 = (2,4,6,8,10)
print("The elements of Tup1 is ", Tup1)
del Tup1
print (Tup1)

Output:

The elements of Tup1 is (2, 4, 6, 8, 10)
Traceback (most recent call last):
File "D:/Python/Tuple Examp 1.py", line 4, in <module>
print (Tup1)
NameError: name 'Tup1' is not defined

Tuple Assignment

Tuple assignment is a powerful feature in Python. It allows a tuple variable on the left of the assignment operator to be assigned to the values on the right side of the assignment operator. Each value is assigned to its respective variable.

Example

>>> (a, b, c) = (34, 90, 76)
>>> print(a,b,c)
34 90 76
# expression are evaluated before assignment
>>> (x, y, z, p) = (2**2, 5/3+4, 15%2, 34>65)
>>> print(x,y,z,p)
4 5.666666666666667 1 False

Note that, when you assign values to a tuple, ensure that the number of values on both sides of the assignment operator are same; otherwise, an error is generated by Python.

Returning multiple values in Tuples

A function can return only one value at a time, but Python returns more than one value from a function. Python groups multiple values and returns them together.

Example : Program to return the maximum as well as minimum values in a list

def Min_Max(n):
	a = max(n)
	b = min(n)
	return(a, b)
Num = (12, 65, 84, 1, 18, 85, 99)
(Max_Num, Min_Num) = Min_Max(Num)
print("Maximum value = ", Max_Num)
print("Minimum value = ", Min_Num)

Output:

Maximum value = 99

Minimum value = 1

Nested Tuples

In Python, a tuple can be defined inside another tuple; called Nested tuple. In a nested tuple, each tuple is considered as an element. The for loop will be useful to access all the elements in a nested tuple.

Example

Toppers = (("Vinodini", "XII-F", 98.7), ("Soundarya", "XII-H", 97.5),
	("Tharani", "XII-F", 95.3), ("Saisri", "XII-G", 93.8))
for i in Toppers:
	print(i)

Output:

('Vinodini', 'XII-F', 98.7)
('Soundarya', 'XII-H', 97.5)
('Tharani', 'XII-F', 95.3)
('Saisri', 'XII-G', 93.8)

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)

(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.

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.