Chapter 1 Class 12 Computer Science Unit 1

Computer Science
Class XII ( As per CBSE Board)
Chapter 1
Revision of the
Basics of Python
New
syllabus
2020-21
Visit : python.mykvs.in for regular updates

Introduction
It is widely used general purpose,high level programming
language.Developed by Guido van Rossum in 1991.
It is used for:
software development,
web development (server-side),
system scripting,
Mathematics.

Features of Python
1. Easy to use – Due to simple syntax rule
2. Interpreted language – Code execution &
interpretation line by line
3. Cross-platform language – It can run on
windows,linux,macinetosh etc. equally
4. Expressive language – Less code to be written as it
itself express the purpose of the code.
5. Completeness – Support wide rage of library
6. Free & Open Source – Can be downloaded freely
and source code can be modify for improvement

Shortcomings of Python
1. Lesser libraries – as compared to other
programming languages like c++,java,.net
2. Slow language – as it is interpreted languages,it
executes the program slowly.
3. Weak on Type-binding – It not pin point on use of a
single variable for different data type.

How to work in Python
(i) in Interactive mode
* Search the python.exe file in the drive in which it is
installed.
If found double click it to start python in interactive
mode

* Click start button -> All programs ->
python<version>->IDLE(Python GUI)

Python command
prompt >>>
Type the following at prompt
print “hello”
print 8*3
print 3**3
k=3+4*3
print k

(ii) in Script mode
Step 1 (Create program file)
Below steps are for simple hello world program
a. Click Start button->All Programs ->
Python<version>->IDLE
b. Now click File->New in IDLE Python Shell
Now type
print “hello”
print “world”
print “python is”,”object oriented programming lang.”
c. Click File->Save and then save the file with filename
and .py extension

(ii) in Script mode
Step 2 (Run program file)
a. Click Open command from IDLE’s File menu and select
the file you have already saved
b. Click Run-> Run Module
c. It will execute all the commands of program file and
display output in separate python shell window
Note :- Python comes in 2 flavours – python 2.x and python 3.x . Later one is
Backward incompatible language as decide by Python Software foundation(PSF).
Mean code written in 2.x will not execute on 3.x . Visit the below link for difference
between 2.x & 3.x
https://www.geeksforgeeks.org/important-differences-between-python-2-x-and-
python-3-x-with-examples/

Data Handling
Most of the computer programming language
support data type, variables,operator and expression like
fundamentals.Python also support these.
Data Types
Data Type specifies which type of value a variable can store.
type() function is used to determine a variable's type in
Python.

Data type continue
Data Types In Python
1. Number
2. String
3. Boolean
4. List
5. Tuple
6. Set
7. Dictionary

Data type continue
1. Number In Python
It is used to store numeric values
Python has three numeric types:
1. Integers
2. Floating point numbers
3. Complex numbers.

Data type continue
1. Integers
Integers or int are positive or negative
numbers with no decimal point. Integers in Python
3 are of unlimited size.
e.g.
a= 100
b= -100
c= 1*20
print(a)
print(b)
print(c)
Output :-
100
-100
200

Data type continue
Type Conversion of Integer
int() function converts any data type to integer.
e.g.
a = "101" # string
b=int(a) # converts string data type to integer.
c=int(122.4) # converts float data type to integer.
print(b)
print(c)Run Code
Output :-
101
122

Data type continue
2. Floating point numbers
It is a positive or negative real numbers with
a decimal point.
e.g.
a = 101.2
b = -101.4
c = 111.23
d = 2.3*3
print(a)
print(b)
print(c)
print(d)Run Code
Output :-
101.2
-101.4
111.23
6.8999999999999995

Data type continue
Type Conversion of Floating point numbers
float() function converts any data type to floating point
number.
e.g.
a='301.4' #string
b=float(a) #converts string data type to floating point number.
c=float(121) #converts integer data type to floating point number.
print(b)
print(c)Run Code
Output :-
301.4
121.0

Data type continue
3. Complex numbers
Complex numbers are combination of a real
and imaginary part.Complex numbers are in the form
of X+Yj, where X is a real part and Y is imaginary part.
e.g.
a = complex(5) # convert 5 to a real part val and zero imaginary part
print(a)
b=complex(101,23) #convert 101 with real part and 23 as imaginary part
print(b)Run Code
Output :-
(5+0j)
(101+23j)

Data type continue
2. String In Python
A string is a sequence of characters. In python we can create string using
single (' ') or double quotes (" ").Both are same in python. e.g.
str='computer science'
print('str-', str) # print string
print('str[0]-', str[0]) # print first char 'h'
print('str[1:3]-', str[1:3]) # print string from postion 1 to 3 'ell'
print('str[3:]-', str[3:]) # print string staring from 3rd char 'llo world'
print('str *2-', str *2 ) # print string two times
print("str +'yes'-", str +'yes') # concatenated string
Output
str- computer science
str[0]- c
str[1:3]- om
str[3:]- puter science
str *2- computer sciencecomputer science
str +'yes'- computer scienceyes

Data type continue
Iterating through string
e.g.
str='comp sc'
for i in str:
print(i)
Output
c
o
m
p
s
c

Data type continue
3. Boolean In Python
It is used to store two possible values either true or
false
e.g.
str="comp sc"
boo=str.isupper() # test if string contains upper case
print(boo)
Output
False

Data type continue
4.List In Python
List are collections of items and each item has its own index value.
5. Tuple In Python
List and tuple, both are same except ,a list is mutable python objects and tuple is
immutable Python objects. Immutable Python objects mean you cannot modify the
contents of a tuple once it is assigned.
e.g. of list
list =[6,9]
list[0]=55
print(list[0])
print(list[1])
OUTPUT
55
9
e.g. of tuple
tup=(66,99)
Tup[0]=3 # error message will be displayed
print(tup[0])
print(tup[1])

Data type continue
6. Set In Python
It is an unordered collection of unique and
immutable (which cannot be modified)items.
e.g.
set1={11,22,33,22}
print(set1)
Output
{33, 11, 22}

Data type continue
7. Dictionary In Python
It is an unordered collection of items and each item
consist of a key and a value.
e.g.
dict = {'Subject': 'comp sc', 'class': '11'}
print(dict)
print ("Subject : ", dict['Subject'])
print ("class : ", dict.get('class'))
Output
{'Subject': 'comp sc', 'class': '11'}
Subject : comp sc
class : 11

Operator
Operators are special symbols in Python that carry out arithmetic or logical
computation. The value that the operator operates on is called the operand.
Arithmetic operators
Used for mathematical operation
Operator Meaning Example
+ Add two operands or unary plus
x + y
+2
- Subtract right operand from the left or unary minus
x - y
-2
* Multiply two operands x * y
/ Divide left operand by the right one (always results into float) x / y
% Modulus - remainder of the division of left operand by the right x % y (remainder of x/y)
//
Floor division - division that results into whole number
adjusted to the left in the number line
x // y
** Exponent - left operand raised to the power of right x**y (x to the power y)

Operator continue
Arithmatic operator continue
e.g.
x = 5
y = 4
print('x + y =',x+y)
print('x - y =',x-y)
print('x * y =',x*y)
print('x / y =',x/y)
print('x // y =',x//y)
print('x ** y =',x**y)
OUTPUT
('x + y =', 9)
('x - y =', 1)
('x * y =', 20)
('x / y =', 1)
('x // y =', 1)
('x ** y =', 625)
• Write a program in python to calculate the simple
interest based on entered amount ,rate and time

Operator continue
# EMI Calculator program in Python
def emi_calculator(p, r, t):
r = r / (12 * 100) # one month interest
t = t * 12 # one month period
emi = (p * r * pow(1 + r, t)) / (pow(1 + r, t) - 1)
return emi
# driver code
principal = 10000;
rate = 10;
time = 2;
emi = emi_calculator(principal, rate, time);
print("Monthly EMI is= ", emi)

Operator continue
How to calculate GST
GST ( Goods and Services Tax ) which is included in netprice of
product for get GST % first need to calculate GST Amount by subtract original
cost from Netprice and then apply
GST % formula = (GST_Amount*100) / original_cost
# Python3 Program to compute GST from original and net prices.
def Calculate_GST(org_cost, N_price):
# return value after calculate GST%
return (((N_price - org_cost) * 100) / org_cost);
# Driver program to test above functions
org_cost = 100
N_price = 120
print("GST = ",end='')
print(round(Calculate_GST(org_cost, N_price)),end='')
print("%")
* Write a Python program to calculate the standard deviation

Operator continue
Comparison operators -used to compare values
> Greater that - True if left operand is greater than the right x > y
< Less that - True if left operand is less than the right x < y
== Equal to - True if both operands are equal x == y
!= Not equal to - True if operands are not equal x != y
>=
Greater than or equal to - True if left operand is greater than or equal to
the right
x >= y
<= Less than or equal to - True if left operand is less than or equal to the right x <= y

Operator continue
Comparison operators continue
e.g.
x = 101
y = 121
print('x > y is',x>y)
print('x < y is',x<y)
print('x == y is',x==y)
print('x != y is',x!=y)
print('x >= y is',x>=y)
print('x <= y is',x<=y)
Output
('x > y is', False)
('x < y is', True)
('x == y is', False)
('x != y is', True)
('x >= y is', False)
('x <= y is', True)

Operator continue
Logical operators
e.g.
x = True
y = False
print('x and y is',x and y)
print('x or y is',x or y)
print('not x is',not x)
Outpur
('x and y is', False)
('x or y is', True)
('not x is', False)
and True if both the operands are true x and y
or True if either of the operands is true x or y
not True if operand is false (complements the operand) not x

Operator continue
Bitwise operators
Used to manipulate bit values.
& Bitwise AND x& y
| Bitwise OR x | y
~ Bitwise NOT ~x
^ Bitwise XOR x ^ y
>> Bitwise right shift x>> 2
<< Bitwise left shift x<< 2

Operator continue
Bitwise operators continue
a = 6
b = 3
print ('a=',a,':',bin(a),'b=',b,':',bin(b))
c = 0
c = a & b;
print ("result of AND is ", c,':',bin(c))
c = a | b;
print ("result of OR is ", c,':',bin(c))
c = a ^ b;
print ("result of EXOR is ", c,':',bin(c))
c = ~a;
print ("result of COMPLEMENT is ", c,':',bin(c))
c = a << 2;
print ("result of LEFT SHIFT is ", c,':',bin(c))
c = a >> 2;
print ("result of RIGHT SHIFT is ", c,':',bin(c))
Output
('a=', 6, ':', '0b110', 'b=', 3, ':', '0b11')
('result of AND is ', 2, ':', '0b10')
('result of OR is ', 7, ':', '0b111')
('result of EXOR is ', 5, ':', '0b101')
('result of COMPLEMENT is ', -7, ':', '-0b111')
('result of LEFT SHIFT is ', 24, ':', '0b11000')
('result of RIGHT SHIFT is ', 1, ':', '0b1')

Operator continue
Python Membership Operators
Test for membership in a sequence
e.g.
a = 5
b = 10
list = [1, 2, 3, 4, 5 ]
if ( a in list ):
print ("Line 1 - a is available in the given list")
else:
print ("Line 1 - a is not available in the given list")
if ( b not in list ):
print ("Line 2 - b is not available in the given list")
else:
print ("Line 2 - b is available in the given list")
Operator Description
in Evaluates to true if it finds a variable in the specified sequence and false otherwise.
not in Evaluates to true if it does not finds a variable in the specified sequence and false otherwise.
output
Line 1 - a is available in the given list
Line 2 - b is not available in the given list

Operator continue
Python Identity Operators
e.g.
a = 10
b = 10
print ('Line 1','a=',a,':',id(a), 'b=',b,':',id(b))
if ( a is b ):
print ("Line 2 - a and b have same identity")
else:
print ("Line 2 - a and b do not have same identity")
OUTPUT
('Line 1', 'a=', 10, ':', 20839436, 'b=', 10, ':', 20839436)
Line 2 - a and b have same identity
Operat
or
Description
is
Evaluates to true if the variables on either side of the operator point to the same
object and false otherwise.
is not
Evaluates to false if the variables on either side of the operator point to the same
object and true otherwise.

Operator continue
Operators Precedence :highest precedence to lowest precedence table
Operator Description
** Exponentiation (raise to the power)
~ + - Complement, unary plus and minus (method names for the last two are +@ and -@)
* / % // Multiply, divide, modulo and floor division
+ - Addition and subtraction
>> << Right and left bitwise shift
& Bitwise 'AND'td>
^ | Bitwise exclusive `OR' and regular `OR'
<= < > >= Comparison operators
<> == != Equality operators
= %= /= //= -= +=
*= **=
Assignment operators
is is not Identity operators
in not in Membership operators
not or and Logical operators

Expression
It is a valid combination of operators,literals and
variable.
1. Arithmatic expression :- e.g. c=a+b
2. Relational expression :- e.g. x>y
3. Logical expression :- a or b
4. String expression :- c=“comp”+”sc”

Type conversion
The process of converting the value of one data type (integer, string, float, etc.) to another
data type is called type conversion.
Python has two types of type conversion.
Implicit Type Conversion
Explicit Type Conversion
Implicit Type Conversion:
In Implicit type conversion, Python automatically converts one data type to another data
type. This process doesn't need any user involvement.
e.g.
num_int = 12
num_flo = 10.23
num_new = num_int + num_flo
print("datatype of num_int:",type(num_int))
print("datatype of num_flo:",type(num_flo))
print("Value of num_new:",num_new)
print("datatype of num_new:",type(num_new))
OUTPUT
('datatype of num_int:', <type 'int'>)
('datatype of num_flo:', <type 'float'>)
('Value of num_new:', 22.23)
('datatype of num_new:', <type 'float'>)

Type conversion
Explicit Type Conversion:
In Explicit Type Conversion, users convert the data type of an object to required
data type. We use the predefined functions like int(),float(),str() etc.
e.g.
num_int = 12
num_str = "45"
print("Data type of num_int:",type(num_int))
print("Data type of num_str before Type Casting:",type(num_str))
num_str = int(num_str)
print("Data type of num_str after Type Casting:",type(num_str))
num_sum = num_int + num_str
print("Sum of num_int and num_str:",num_sum)
print("Data type of the sum:",type(num_sum))
OUTPUT
('Data type of num_int:', <type 'int'>)
('Data type of num_str before Type Casting:', <type 'str'>)
('Data type of num_str after Type Casting:', <type 'int'>)
('Sum of num_int and num_str:', 57)
('Data type of the sum:', <type 'int'>)

math module
It is a standard module in Python. To use mathematical functions of this module,we
have to import the module using import math.
Function Description Example
ceil(n) It returns the smallest integer greater than or equal to n. math.ceil(4.2) returns 5
factorial(n) It returns the factorial of value n math.factorial(4) returns 24
floor(n) It returns the largest integer less than or equal to n math.floor(4.2) returns 4
fmod(x, y) It returns the remainder when n is divided by y math.fmod(10.5,2) returns 0.5
exp(n) It returns e**n math.exp(1) return 2.718281828459045
log2(n) It returns the base-2 logarithm of n math.log2(4) return 2.0
log10(n) It returns the base-10 logarithm of n math.log10(4) returns 0.6020599913279624
pow(n, y) It returns n raised to the power y math.pow(2,3) returns 8.0
sqrt(n) It returns the square root of n math.sqrt(100) returns 10.0
cos(n) It returns the cosine of n math.cos(100) returns 0.8623188722876839
sin(n) It returns the sine of n math.sin(100) returns -0.5063656411097588
tan(n) It returns the tangent of n math.tan(100) returns -0.5872139151569291
pi It is pi value (3.14159...) It is (3.14159...)
e It is mathematical constant e (2.71828...) It is (2.71828...)

Control Statements
Control statements are used to control the flow of
execution depending upon the specified condition/logic.
There are three types of control statements.
1. Decision Making Statements
2. Iteration Statements (Loops)
3. Jump Statements (break, continue, pass)

Decision Making Statement
Decision making statement used to control the flow
of execution of program depending upon condition.
There are three types of decision making statement.
1. if statements
2. if-else statements
3. Nested if-else statement

1. if statements
An if statement is a programming conditional
statement that, if proved true, performs a function
or displays information.

1. if statements
Syntax:
if(condition):
statement
[statements]
e.g.
noofbooks = 2
if (noofbooks == 2):
print('You have ')
print(‘two books’)
print(‘outside of if statement’)
Output
You have two books
Note:To indicate a block of code in Python, you must indent each line of
the block by the same amount. In above e.g. both print statements are
part of if condition because of both are at same level indented but not
the third print statement.

1. if statements
Using logical operator in if statement
x=1
y=2
if(x==1 and y==2):
print(‘condition matcing the criteria')
Output :-
condition matcing the criteria
-----------------------------------------------------------
a=100
if not(a == 20):
print('a is not equal to 20')
Output :-
a is not equal to 20

2. if-else Statements
If-else statement executes some code if the test expression is true
(nonzero) and some other code if the test expression is false.

2. if-else Statements
Syntax:
if(condition):
statements
else:
statements
e.g.
a=10
if(a < 100):
print(‘less than 100')
else:
print(‘more than equal 100')
OUTPUT
less than 100
*Write a program in python to check that entered numer is even or odd

The nested if...else statement allows you to check for multiple test
expressions and execute different codes for more than two
conditions.

Syntax
If (condition):
statements
elif (condition):
statements
else:
statements
E.G.
num = float(input("Enter a number: "))
if num >= 0:
if num == 0:
print("Zero")
else:
print("Positive number")
else:
print("Negative number")
OUTPUT
Enter a number: 5
Positive number
* Write python program to find out largest of 3 numbers.

Iteration Statements (Loops)
Iteration statements(loop) are used to execute a block of
statements as long as the condition is true.
Loops statements are used when we need to run same code
again and again.
Python Iteration (Loops) statements are of three type :-
1. While Loop
2. For Loop
3. Nested For Loops

1. While Loop
It is used to execute a block of statement as long as a given
condition is true. And when the condition become false, the
control will come out of the loop. The condition is checked every
time at the beginning of the loop.
Syntax
while (condition):
statement
[statements]
e.g.
x = 1
while (x <= 4):
print(x)
x = x + 1
Output
1
2
3
4

While Loop continue
While Loop With Else
e.g.
x = 1
while (x < 3):
print('inside while loop value of x is ',x)
x = x + 1
else:
print('inside else value of x is ', x)
Output
inside while loop value of x is 1
inside while loop value of x is 2
inside else value of x is 5
*Write a program in python to find out the factorial of a given number

While Loop continue
Infinite While Loop
e.g.
x = 5
while (x == 5):
print(‘inside loop')
Output
Inside loop
Inside loop
…
…

2. For Loop
It is used to iterate over items of any sequence, such as a list
or a string.
Syntax
for val in sequence:
statements
e.g.
for i in range(3,5):
print(i)
Output
3
4

2. For Loop continue
Example programs
for i in range(5,3,-1):
print(i)
Output
5
4
range() Function Parameters
start: Starting number of the sequence.
stop: Generate numbers up to, but not including this number.
step(Optional): Determines the increment between each numbers in the
sequence.

For Loop With Else
e.g.
for i in range(1, 4):
print(i)
else: # Executed because no break in for
print("No Break")
Output
1
2
3
4
No Break Visit : python.mykvs.in for regular updates

Nested For Loop
e.g.
for i in range(1,3):
for j in range(1,11):
k=i*j
print (k, end=' ')
print()
Output
1 2 3 4 5 6 7 8 9 10
2 4 6 8 10 12 14 16 18 20

3. Jump Statements
Jump statements are used to transfer
the program's control from one location to another. Means
these are used to alter the flow of a loop like - to skip a part
of a loop or terminate a loop
There are three types of jump statements used in python.
1.break
2.continue
3.pass

1.break
it is used to terminate the loop.
e.g.
for val in "string":
if val == "i":
break
print(val)
print("The end")
Output
s
t
r
The end

2.continue
It is used to skip all the remaining statements in the
loop and move controls back to the top of the loop.
e.g.
for val in "init":
if val == "i":
continue
print(val)
print("The end")
Output
n
t
The end

3. pass Statement
This statement does nothing. It can be used when a statement is
required syntactically but the program requires no action.
Use in loop
while True:
pass # Busy-wait for keyboard interrupt (Ctrl+C)
In function
It makes a controller to pass by without executing any code.
e.g.
def myfun():
pass #if we don’t use pass here then error message will be shown
print(‘my program')
OUTPUT
My program

3. pass Statement continue
e.g.
for i in 'initial':
if(i == 'i'):
pass
else:
print(i)
OUTPUT
n
t
a
L
NOTE : continue forces the loop to start at the next iteration
while pass means "there is no code to execute here" and
will continue through the remainder or the loop body.

Chapter 1 Class 12 Computer Science Unit 1

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