Chapter 3 :

Informatics
Practices
Class XI ( As per Python
CBSE Board) Fundamentals

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Introduction
Python 3.0 was released in 2008. Although this version is
supposed to be backward incompatibles, later on many of its
important features have been back ported to be compatible
with version 2.7
Python Character Set
A set of valid characters recognized by python. Python uses the traditional
ASCII character set. The latest version recognizes the Unicode character set.
The ASCII character set is a subset of the Unicode character set
Letters :– A-Z,a-z
Digits :– 0-9
Special symbols :– Special symbol available over keyboard
White spaces:– blank space,tab,carriage return,new line, form feed
Other characters:- Unicode

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Input and Output
var1=‘Computer Science'
var2=‘Informatics Practices'
print(var1,' and ',var2,' )
Output :-
Computer Science and Informatics Practices

raw_input() Function In Python allows a user to give input to a program

from a keyboard but in the form of string.
NOTE : raw_input() function is deprecated in python 3
e.g.
age = int(raw_input(‘enter your age’))
percentage = float(raw_input(‘enter percentage’))
input() Function In Python allows a user to give input to a program from
a keyboard but returns the value accordingly.
e.g.
age = int(input(‘enter your age’))
C = age+2 #will not produce any error
NOTE : input() function always enter string value in python 3.so
on need int(),float() function can be used for data conversion.

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Token

Smallest individual unit in a program is known as token.

1. Keywords
2. Identifiers
3. Literals
4. Operators
5. punctuators

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Keywords
Reserve word of the compiler/interpreter which can’t be
used as identifier.

and exec not

as finally or

assert for pass

break from print

class global raise

continue if return

def import try

del in while

elif is with

else lambda yield

except

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Identifiers
A Python identifier is a name used to identify a variable,
function, class, module or other object.
* An identifier starts with a letter A to Z or a to z or an
underscore (_) followed by zero or more letters, underscores
and digits (0 to 9).
* Python does not allow special characters
* Identifier must not be a keyword of Python.
* Python is a case sensitive programming language.
Thus, Rollnumber and rollnumber are two different identifiers
in Python.
Some valid identifiers : Mybook, file123, z2td, date_2, _no
Some invalid identifier : 2rno,break,my.book,data-cs

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Identifiers-continue
Some additional naming conventions
1. Class names start with an uppercase letter. All other
identifiers start with a lowercase letter.

2. Starting an identifier with a single leading underscore

indicates that the identifier is private.

3. Starting an identifier with two leading underscores

indicates a strong private identifier.

4. If the identifier also ends with two trailing

underscores, the identifier is a language-defined
special name.

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Literals
Literals in Python can be defined as number, text, or
other data that represent values to be stored in variables.

Example of String Literals in Python

name = ‘Johni’ , fname =“johny”

Example of Integer Literals in Python(numeric literal)

age = 22

Example of Float Literals in Python(numeric literal)

height = 6.2

Example of Special Literals in Python

name = None
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Literals
Escape sequence
Escape Sequence Description

\\ Backslash (\)

\' Single quote (')

\" Double quote (")

\a ASCII Bell (BEL)

\b ASCII Backspace (BS)

\f ASCII Formfeed (FF)

\n ASCII Linefeed (LF)

\r ASCII Carriage Return (CR)

\t ASCII Horizontal Tab (TAB)

\v ASCII Vertical Tab (VT)

\ooo Character with octal value ooo

\xhh Character with hex value hh

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Operators
Operators can be defined as symbols that are used to perform
operations on operands.

Types of Operators

1. Arithmetic Operators.
2. Relational Operators.
3. Assignment Operators.
4. Logical Operators.
5. Bitwise Operators
6. Membership Operators
7. Identity Operators

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Operators continue
1. Arithmetic Operators
Arithmetic Operators are used to perform arithmetic operations like
addition, multiplication, division etc.
Operators Description Example

+ perform addition of two number a+b

- perform subtraction of two number a-b

/ perform division of two number a/b

* perform multiplication of two number a*b

% Modulus = returns remainder a%b

Floor Division = remove digits after the

// a//b
decimal point

** Exponent = perform raise to power a**b

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Operators continue
2. Relational Operators
Relational Operators are used to compare the values.

Operators Description Example

== Equal to, return true if a equals to b a == b

!= Not equal, return true if a is not equals to b a != b

Greater than, return true if a is greater than

> a>b
b

Greater than or equal to , return true if a is

>= a >= b
greater than b or a is equals to b

< Less than, return true if a is less than b a<b

Less than or equal to , return true if a is

<= a <= b
less than b or a is equals to b

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Operators continue
3. Assignment Operators
Used to assign values to the variables.
Operators Description Example

= Assigns values from right side operands to left side operand a=b

+= Add 2 numbers and assigns the result to left operand. A+=b

/= Divides 2 numbers and assigns the result to left operand. a/=b

*= Multiply 2 numbers and assigns the result to left operand. a*=b

-= Subtracts 2 numbers and assigns the result to left operand. a-=b

%= modulus 2 numbers and assigns the result to left operand. a%=b

//= Perform floor division on 2 numbers and assigns the result to left operand. a//=b

**= calculate power on operators and assigns the result to left operand. a**=b

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Operators continue
4. Logical Operators
Logical Operators are used to perform logical operations on the
given two variables or values.

Operators Description Example

and return true if both condition are true x and y

or return true if either or both condition are true x or y

not reverse the condition not(a>b)

a=30
b=20
if(a==30 and b==20):
print('hello')

Output :-
hello

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Operators continue
6. Membership Operators
The membership operators in Python are used to validate whether a
value is found within a sequence such as such as strings, lists, or
tuples.
Operators Description Example

in return true if value exists in the sequence, else false. a in list

not in return true if value does not exists in the sequence, else false. a not in list

E.g.
a = 22
list = [22,99,27,31]
In_Ans = a in list
NotIn_Ans = a not in list
print(In_Ans)
print(NotIn_Ans)
Output :-
True
False
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Operators continue
7. Identity Operators
Identity operators in Python compare the memory locations of two
objects.

Operators Description Example

is returns true if two variables point the same object, else false a is b

is not returns true if two variables point the different object, else false a is not b

a = 37
b=34
if (a is b):
print('both a and b has same identity')
else:
print('a and b has different identity')

Output :-
both a and b has different identity

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Punctuators
Used to implement the grammatical and structure of a Syntax.Following
are the python punctuators.

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Barebone of a python program
#function definition comment
def keyArgFunc(empname, emprole):
print ("Emp Name: ", empname) Function
print ("Emp Role: ", emprole) indentation
return;
A = 20 expression
print("Calling in proper sequence")
keyArgFunc(empname = "Nick",emprole = "Manager" )
print("Calling in opposite sequence") statements
keyArgFunc(emprole = "Manager",empname = "Nick")

A python program contain the following components

a. Expression
b. Statement
c. Comments
d. Function
e. Block &n indentation

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Barebone of a python program
a. Expression : - which is evaluated and produce result. E.g. (20 + 4) / 4
b. Statement :- instruction that does something.
e.g
a = 20
print("Calling in proper sequence")
c. Comments : which is readable for programmer but ignored by python
interpreter
i. Single line comment: Which begins with # sign.
ii. Multi line comment (docstring): either write multiple line beginning with #
sign or use triple quoted multiple line. E.g.
‘’’this is my
first
python multiline comment
‘’’
d. Function
a code that has some name and it can be reused.e.g. keyArgFunc in
above program
d. Block & indentation : group of statements is block.indentation at same
level create a block.e.g. all 3 statement of keyArgFunc function
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Variables
Variable is a name given to a memory location. A variable can consider as a
container which holds value. Python is a type infer language that means you
don't need to specify the datatype of variable.Python automatically get
variable datatype depending upon the value assigned to the variable.
Assigning Values To Variable
name = ‘python' # String Data Type
sum = None # a variable without value
a = 23 # Integer
b = 6.2 # Float
sum = a + b
print (sum)
Multiple Assignment: assign a single value to many variables
a = b = c = 1 # single value to multiple variable
a,b = 1,2 # multiple value to multiple variable
a,b = b,a # value of a and b is swaped

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Variables
Variable Scope And Lifetime in Python Program
1. Local Variable
def fun():
x=8
print(x)

fun()
print(x) #error will be shown
2. Global Variable
x=8
def fun():
print(x) # Calling variable ‘x’ inside fun()

fun()
print(x) # Calling variable ‘x’ outside fun()

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Dynamic typing

Data type of a variable depend/change upon the value assigned to a

variable on each next statement.
X = 25 # integer type
X = “python” # x variable data type change to string on just next line
Now programmer should be aware that not to write like this:
Y = X / 5 # error !! String cannot be devided

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Input and Output
print() Function In Python is used to print output on the screen.
Syntax of Print Function
print(expression/variable)
e.g.
print(122)
Output :-
122

print('hello India')
Output :-
hello India

print(‘Computer',‘Science')
print(‘Computer',‘Science',sep=' & ')
print(‘Computer',‘Science',sep=' & ',end='.')
Output :-
Computer Science
Computer & Science
Computer & Science.

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