Python for Class XII

1. Chapter 2
Revision of the Basics of Python - II
Class – XII
Subject: Computer Science

2. Tuples
 Its Sequence of values of any data type enclosed
in round brackets.
 Tuples are Immutable .
 Examples:-
 () is a tuple with no element
 (6, ) is a tuple with one element
 (‘a’, 2, 5.77) is a tuple of mixed data types

3. Creating Tuples
 By enclosing values in parentheses
 A = (1,2,3)
 B = (“Ram”, “Sham”, “Anil”)
 Using function tuple(<any sequence>)
 A = tuple(“WELCOME”)
 B=tuple([1,2,3,4])
 C = tuple(input(“enter any sequence”))
 Using eval()
 Most common method used to create tuple
 A = eval(“(1,2,3,4)”)

4. Similarities with Lists
 len() function
 Returns number of elements in tuple and list both
 Indexing and slicing
 Indexing and Slicing is same in list and tuple
 Membership operators
 ‘in’ and ‘not in’ operators work similarly for tuple and lists
 + and * operators
 Concatenation and Replication
 Traversing
 Traversing list and tuple is same
 for <Item> in <tuple/list> :
Process <item>

5. Similarities with Lists
 Unpacking
 Unpacking is same for lists and tuples
 E.g. A = (1,2,3,4)
 X,Y,Z,W = A
 Count() method
 Count() method works similarly for lists and tuples

6. Differences with Lists
 As tuple is immutable, Changing tuple elements
is not allowed
 e.g. A= (1,2,3)
 A[2] = 4 # this is not allowed
 Adding or deleting elements in tuple is not
allowed
 max() and min() functions for tuples
 max(<tuple>) gives maximum value in tuple
 min(<tuple>) gives minimum value in a tuple
 max() and min() works only if all the elements of
tuple are of same data type

7. Copying A list
 How to create a copy of a List?
 Lets say we have a list
 L = [1,2,3,4]
How to create a copy L_Copy of this
list L???
 L_Copy = list(L)

8. List Reverse and Sort
 Function List.reverse() is used to reverse a list
 Function List.sort() is used to sort a list
 By default sorting is done in which order?
 Increasing order
 How to do sorting in decreasing order ?
 List.sort(reverse = True)

9. Dictionary
 Dictionary in python is an unordered pair of keys:
values
 Dictionary is not a sequence, its not indexed by
using numbers
 Dictionary is created using curly braces ( { } )
 Dictionary is indexed by using Keys
 Dictionary keys are immutable and all the keys
should be unique
 Dictionary is a mutable data object, Its values can
be changed (not keys)

10. How to create Dictionary
 Simply by enclosing Key:Value pairs in curly
braces
 D1 = { 1 : “David” , 2 : “Rick , 3: “Kiya” }
 D2 = {} #this is an empty dictionary
 By adding key:value pairs in an empty dictionary
 D2 = {}
 D2[1] = ‘A’
 It will create dictionary D2 = {1:’A’}

11. Creating dictionary : dict() function
 Dictionary can be created by passing key and value
pairs to dict() function. There are multiple ways to do
so—
 1. By passing arguments and values
 D1 = dict(rollno = 1, name = ‘Ajay’, marks = 90)
 2. By passing keys and values using zip function
 D1 = dict(zip(‘rollno’,’name’,’marks’ ), (1,’Ajay’,90))
 3. By passing key:value pair in the form of sequence
 D1 = dict([[‘rollno’ ,1],[‘name’,’Ajay’],[‘Marks’,90]]

12. Traversing Dictionary
 for <Item> in <Dictionary>
Process <Item>
#Here <Item> will be assigned the keys of dictionary
D1 = {1 : ‘A’, 2: ‘B’, 3 : ‘C’ }
for i in D1:
print( i , D1[i}

13. Adding and Updating elements of
Dictionary ? How?
 D1 = {‘RollNo’ : 1, ‘Name’ : ‘Ajay’}
 How to add new key value pair as “Marks” : 90??
 D1[“Marks”] = 90
 How to update Marks to 95??
 D1[“Marks”] = 95

14. Deleting elements of dictionary
 1. using del command
 del <dictionary>[<key>]
 If <key> does not exist in <dictionary> python will throw error
 del D1[‘Marks’]
 del D1 #It will delete entire D1 dictionary object
 2. Using pop() method
 <dictionary>.pop(<key>)
 D1.pop(‘Marks’)
 If <key> does not exist , python will throw error
 But you can give your own error message
 D1.pop(‘Marks’, “Not Found”)

15. Membership Operators for Dictionary
 How in and not in operator works for dictionaries?
 in and not in operator checks for existence of keys
in dictionary
 in operator will return True if given KEY exist in
dictionary
 not in operator will return True if given KEY does
not exist in dictionary

16. Methods for Dictionaries
1. len(<dictionary>) : It gives length of
dictionary(number of pairs )
2. <dictionary>.clear(): It gives empty dictionary
3. <dictionary>.get(<key>) : to get value for a Key
4. <dictionary>.items(): it gives sequence of
tuples(key, value)
5. <dictionary>.keys() : It returns all keys as a list
6. <dictionary>.values(): It returns all values a a list
7. <dictionary>.update() : this method merges two
dictionaries