Computer Science
Class -XI
Code No. 083
2023-24




CLASS-XI
SUBJECT: COMPUTER SCIENCE (083) – PYTHON
INDEX
NO. CHAPTER NAME 
1 INTRODUCTION TO PYTHON 
2 PYTHON FUNDAMENTALS  





CHAPTER-2
PYTHON FUNDAMENTALS
2.1 Python Character Set :
It is a set of valid characters that a language recognize.
Letters: A-Z, a-z
Digits : 0-9
Special Symbols
Whitespace
2.2 TOKENS
Token: Smallest individual unit in a program is known as 
token.
There are five types of token in python:
1. Keyword
2. Identifier
3. Literal
4. Operators
5. Punctuators
1. Keyword: Reserved words in the library of a language. 
There are 33 keywords in python.
False class finally is return break
None continue for lambda try except
True def from nonlocal while in
and del global not with raise
as elif if or yield
assert else import pass
All the keywords are in lowercase except 03 keywords 
(True, False, None).

2. Identifier: The name given by the user to the 
entities like variable name, class-name,
function-name etc.

B. String literals:
String literals can be formed by enclosing a text 
in the quotes. We can use both single as
well as double quotes for a String.
Eg:
"Aman" , '12345'
Escape sequence characters:
\\ Backslash
\’ Single quote
\” Double quote
\a ASCII Bell
\b Backspace
\f ASCII Formfeed
\n New line charater
\t Horizontal tab
C. Boolean literal: A Boolean literal can have any 
of the two values: True or False.
D. Special literals: Python contains one special
literal i.e. None.
None is used to specify to that field that is not 
created. It is also used for end of lists in
Python.
E. Literal Collections: Collections such as tuples,
lists and Dictionary are used in Python.
4. Operators: An operator performs the operation 
on operands. Basically there are two
types of operators in python according to number 
of operands:
A. Unary Operator
B. Binary Operator
A. Unary Operator: Performs the operation on one 
operand.

Example:
+ Unary plus
- Unary minus
~ Bitwise complement
not Logical negation
B. Binary Operator: Performs operation on two operands.
5. Separator or punctuator : , ; , ( ), { }, [ ]
2.3 Mantissa and Exponent Form:
A real number in exponent form has two parts:
 mantissa
 exponent
Mantissa : It must be either an integer or a proper 
real constant.
Exponent : It must be an integer. Represented by a 
letter E or e followed by integer value.
Valid Exponent form Invalid Exponent form
123E05 2.3E (No digit specified for exponent)
0.24E3.2 (Exponent cannot have fractional part)
23,455E03 (No comma allowed)
1.23E07
0.123E08
123.0E08
123E+8
1230E04
-0.123E-3
163.E4
.34E-2
4.E3

2.4 Basic terms of a Python Programs:
A. Blocks and Indentation
B. Statements
C. Expressions
D. Comments
A. Blocks and Indentation:
 Python provides no braces to indicate blocks of code
for class and function definition or
flow control.
 Maximum line length should be maximum 79 characters.
 Blocks of code are denoted by line indentation, which 
is rigidly enforced.
 The number of spaces in the indentation is variable, 
but all statements within the block
must be indented the same amount.
for example –
if True:
print(“True”)
else:
print(“False”)
B. Statements
A line which has the instructions or expressions.
C. Expressions:
A legal combination of symbols and values that produce 
a result. Generally it produces a value.
D. Comments: Comments are not executed. Comments 
explain a program and make a
program understandable and readable. All characters 
after the # and up to the end of the
physical line are part of the comment and the Python 
interpreter ignores them.

There are two types of comments in python:
i. Single line comment
ii. Multi-line comment
i. Single line comment: This type of comments start 
in a line and when a line ends, it is
automatically ends. Single line comment starts with 
# symbol.
Example: if a>b: # Relational operator compare two values
ii. Multi-Line comment: Multiline comments can be written 
in more than one lines. Triple
quoted ‘ ’ ’ or “ ” ”) multi-line comments may be used 
in python. It is also known as
docstring.
Example:
‘’’ This program will calculate the average of 10 values.
First find the sum of 10 values
and divide the sum by number of values
‘’’

Multiple Statements on a Single Line:
The semicolon ( ; ) allows multiple statements on the 
single line given that neither statement
starts a new code block.
Example:-
x=5; print(“Value =” x)
2.5 Variable/Label in Python:
Definition: Named location that refers to a value and 
whose value can be used and processed
during program execution.
Variables in python do not have fixed locations. The 
location they refer to changes every time
their values change.
Creating a variable:
A variable is created the moment you first assign a 
value to it.
Example:
x = 5
y = “hello”
Variables do not need to be declared with any particular 
type and can even change type after
they have been set. It is known as dynamic Typing.
x = 4 # x is of type int
x = "python" # x is now of type str
print(x)
Rules for Python variables:
 A variable name must start with a letter or the 
underscore character
 A variable name cannot start with a number
 A variable name can only contain alpha-numeric 
characters and underscore (A-z, 0-9,
and _ )
 Variable names are case-sensitive (age, Age and AGE 
are three different variables)

Python allows assign a single value to multiple variables.
Example: x = y = z = 5
You can also assign multiple values to multiple variables.
For example −
x , y , z = 4, 5, “python”
4 is assigned to x, 5 is assigned to y and string 
“python” assigned to variable z respectively.
x=12
y=14
x,y=y,x
print(x,y)
Now the result will be
14 12
Lvalue and Rvalue:
An expression has two values. Lvalue and Rvalue.
Lvalue: the LHS part of the expression
Rvalue: the RHS part of the expression
Python first evaluates the RHS expression and then assigns to LHS.
Example:
p, q, r= 5, 10, 7
q, r, p = p+1, q+2, r-1
print (p,q,r)
Now the result will be:
6 6 12
Note: Expressions separated with commas are evaluated from 
left to right and assigned in same
order.
 If you want to know the type of variable, you can use 
type( ) function :

Syntax:
type (variable-name)
Example:
x=6
type(x)
The result will be:

 If you want to know the memory address or location 
of the object, you can use id( )
function.
Example:
>>>id(5)
1561184448
>>>b=5
>>>id(b)
1561184448
You can delete single or multiple variables by using del statement. 
Example:
del x
del y, z
2.6 Input from a user:
input( ) method is used to take input from the user.
Example:
print("Enter your name:")
x = input( )
print("Hello, " + x)
 input( ) function always returns a value of string type.
2.7 Type Casting:
To convert one data type into another data type.
Casting in python is therefore done using constructor functions:

 int( ) - constructs an integer number from an integer literal, 
a float literal or a string
literal.
Example:
x = int(1) # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3
 float( ) - constructs a float number from an integer literal,
a float literal or a string literal.
Example:
x = float(1) # x will be 1.0
y = float(2.8) # y will be 2.8
z = float("3") # z will be 3.0
w = float("4.2") # w will be 4.2
 str( ) - constructs a string from a wide variety of data 
types, including strings, integer
literals and float literals.
Example:
x = str("s1") # x will be 's1'
y = str(2) # y will be '2'
z = str(3.0) # z will be '3.0'
Reading a number from a user:
x= int (input(“Enter an integer number”))
2.8 OUTPUT using print( ) statement:
Syntax:
print(object, sep=, end=)
object : It can be one or multiple objects separated by comma.
sep : sep argument specifies the separator character or string. 
It separate the objects/items. By
default sep argument adds space in between the items when printing.
end : It determines the end character that will be printed at
the end of print line. By default it
has newline character( ‘\n’ ).
Example:
x=10
y=20
z=30
print(x,y,z, sep=’@’, end= ‘ ‘)
Output:
10@20@30