CH-3 FEATURES OF PYTHON, data types token

Python Character
Set
Is a set of valid characters that python can recognize. A
character represent letters, digits or any symbol. Python
support UNICODE encoding standard. Following are the
Python character set
 Letter
s
 Digits
: A-Z, a-z
: 0-9
 Special symbols :space +-*/()~`!@#$%^ & [{
]};:‟”,<.>/?
 White spaces : Blank space, Enter,
Tab
 Other character : python can process all
ASCII and UNICODE as a part of data or literal

TOKENS
In a passage of text, individual words and
punctuation marks are called tokens or lexical units
or lexical elements. The smallest individual unit in a
program is known as Tokens. Python has
following tokens:
 Keywords
 Identifiers(Name)
 Literals
 Operators
 Punctuators

KEYWORDS
VINOD KUMAR VERMA, PGT(CS), KV OEF
KANPUR &
SACHIN BHARDWAJ, PGT(CS), KV NO.1 TEZPUR
Keywords are the reserved words and have special
meaning for python interpreter. Every keyword is
assigned specific work and it can be used only for
that purpose.
A partial list of keywords in Python is

IDENTIFIERS
Are the namesgiven to differentparts of program like
variables, objects, classes, functions etc.
Identifier forming rules of Python are :
 Is an arbitrarily long sequence of letters and digits
 The first character must be letter or underscore
 Upper and lower case are different
 The digits 0-9 are allowed except for first character
 It must not be a keyword
 No special characters are allowed other than underscore is
allowed.
 Space not allowed

GradePay
GRADEPA
Y
File_12_2018
_ismarried
JAMES007
_to_updat
e
The following are some valid identifiers
The following are some invalid identifiers

Literals /
Values
 Literals are data items that have a fixed
value. Python supports several kinds of
literals:
🞑 String Literal
🞑 Numeric Literals
🞑 Boolean Literals
🞑 Special Literals – None
🞑 Literal Collections

String
Literals
 It is a collection of character(s) enclosed in a
double or single quotes
 Examples of String literals
🞑 “Python”
🞑 “Mogambo”
🞑 „123456‟
🞑 „Hello How are your‟
🞑 „$‟, „4‟,”@@”
 In Python both single character or multiple
characters enclosed in quotes such as “kv”,
„kv‟,‟*‟,”+” are treated as same

Non-Graphic (Escape)
characters
 They are the special characters which cannot
be type directly from keyboard like backspace,
tabs, enter etc. When the characters are typed
they perform some action. These are
represented by escape characters. Escape
characters are always begins from backslash()
character
.

List of Escape
characters
Escape Sequence What it does Escape Sequence What it does
Backslash r Carriage return
‟ Single quotes t Horizontal tab
” Double quotes uxxxx Hexadecim
al value(16
bit)
a ASCII bell Uxxxx Hexadecim
al value(32
bit)
b Back Space v vertical tab
n New line ooo Octal value

String type in
Python
 Python allows you to have two string types:
🞑 Single Line Strings
 The string we create using single or double quotes are
normally single-line string i.e. they must terminate in
one line.
 For e.g if you type as
 Name="KV and press enter
 Python we show you an error “EOL while scanning string
literal”
 The reason is quite clear, Python by default creates single-line
string with both single quotes and it must terminate in the same
line by quotes

String type in
Python
 Multiline String
🞑 Some times we need to store some text across
multiple lines. For that Python offers multiline
string.
🞑 T
o store multiline string Python provides two ways:
(a) By adding a backslash at the end of normal Single /
Double
quoted string. For e.g.
>>> Name="1/6 Mall Road
Kanpur"
>>> Name
'1/6 Mall RoadKanpur'
>>>

String type in
Python
 Multiline String
(b) By typing text in triple quotation
marks
for e.g.
>>> Address="""1/7 Preet
Vihar New Delhi
India"""
>>> print(Address)
1/7 Preet Vihar
New Delhi
India
>>> Address
'1/7 Preet Vihar
nNew Delhi
nIndia'

Size of
String
 Python determines the size of string as the count of characters in the
string. For example size of string “xyz” is 3 and of “welcome” is 7. But
if your string literal has an escape sequence contained in it then make
sure to count the escape sequence as one character. For e.g.
 You can check these size using len() function of Python. For
example
 >>>len(„abc )
‟ and press enter, it will show the size as 3
String Size
„‟ 1
„abc‟ 3
„ab‟ 2
“Meera‟s Toy” 11
“Vicky‟s” 7

Size of
String
 For multiline strings created with triple quotes : while calculating
size the EOL character as the end of line is also counted in the
size. For example, if you have created String Address as:
>>> Address="""Civil
lines Kanpur"""
>>> len(Address)
18
 For multiline string created with single/double quotes the EOL is
not counted.
>>>
data="ab
bc
cd"
>>>
len(data) 6

Numeric
Literals
 The numeric literals in Python can belong to
any of the following numerical types:
1)Integer Literals: it contain at least one digit and
must not contain decimal point. It may contain (+)
or (-) sign.
🞑 Types of Integer Literals:
a) Decimal : 1234, -50, +100
b)Octal : it starts from symbol 0o (zero followed
by letter ‘o’)
 For e.g. 0o10 represent decimal 8

Numeric
Literals
>>> num = 0o10
>>> print(num)
It will print the value 8
c) Hexadecimal : it starts from 0x (zero followed
by letter ‘x’)
>>> num = 0oF
>>> print(num)
it will print the value 15

Numeric
Literals
 2) Floating point Literals: also known as real
literals. Real literals are numbers having fractional
parts. It is represented in two forms Fractional
Form or Exponent Form
 Fractional Form: it is signed or unsigned with decimal
point
🞑 For e.g. 12.0, -15.86, 0.5, 10. (will represent 10.0)
 Exponent Part: it consists of two parts “Mantissa”
and “Exponent”.
🞑 For e.g. 10.5 can be represented as 0.105 x 102 =
0.105E02 where
0.105 is mantissa and 02 (after letter E) is exponent

Points to
remember
<class
'tuple'>
 Numeric values with commas are not considered int or float value, rather
Python treats them as tuple. Tuple in a python is a collection of values or
sequence of values. (will be discussed later on)
 You can check the type of literal using type() function. For e.g.
>>> a=100
>>> type(a)
<class 'int'>
>>> b=10.5
>>> type(b)
<class 'float'>
>>> name="hello“
>>> type(name)
<class 'str'>
>>> a=100,50,600
>>> type(a)

Boolean
Literals
A Boolean literals in Python is used to represent one of
the two Boolean values i.e. True or False
These are the only two values supported for Boolean
Literals For e.g.
>>> isMarried=True
>>> type(isMarried)
<class 'bool'>

Special Literals
None
Python has one special literal, which is None. It indicate
absence of value. In other languages it is knows as NULL.
It is also used to indicate the end of lists in Python.
>>> salary=None
>>> type(salary)
<class 'NoneType'>

Complex
Numbers
Complex: Complex number in python is made up of two floating point
values, one each for real and imaginary part. For accessing different
parts of variable (object) x; we will use x.real and x.image. Imaginary
part of the number is represented by “j” instead of “I”, so 1+0j
denotes zero imaginary.
part.
Example
>>> x = 1+0j
>>> print
x.real,x.imag 1.0 0.0
Example
>>> y = 9-5j
>>> print y.real,
y.imag 9.0 -5.0

Conversion from one type to
another
 Python allows converting value of one data type to another
data type. If it is done by the programmer then it will be
known as type conversion or type casting and if it is done by
compiler automatically then it will be known as implicit type
conversion.
Example of Implicit type conversion
>>> x = 100
>>> type(x)
<type 'int'>
>>> y = 12.5
>>> type(y)
<type 'float'>
>>> x=y
>>> type(x)
<type 'float'> # Here x is automatically converted to float

Conversion from one type to
another
Explicit type conversion
T
o perform explicit type conversion Python provide
functions like int(), float(), str(), bool()
>>> a=50.25
>>> b=int(a)
>>> print
b 50
Here 50.25
is
converted
to int
value 50
>>>a=25
>>>y=floa

Simple Input and
Output
 In python we can take input from user using the built-in
function input().
 Syntax
variable = input(<message to display>)
Note: value taken by input() function will always be of String type,
so by
default you will not be able to perform any arithmetic operation on
variable.
>>> marks=input("Enter your
marks ") Enter your marks 100
>>> type(marks)
<class 'str'>
Here you can seeeven we are entering value 100 but it will be treated
as string and will not allow any arithmetic operation

Simple Input and
Output
>>> salary=input("Enter your
salary ") Enter your salary 5000
>>> bonus = salary*20/100
Traceback (most recent call
last):
File "<stdin>", line 1, in
<module>
TypeError: unsupported operand
type(s) for /: 'str' and 'int'

Reading / Input of
Numbers
 Now we are aware that input() function value
will always be of string type, but what to do if
we want number to be entered. The solution to
this problem is to convert values of input() to
numeric type using int() or float() function.

Possible chances of error while
taking input as numbers
1. Entering float value while converting
to int
>>> num1=int(input("Enter marks
")) Enter marks 100.5
Traceback (most recent call last):
File "<stdin>", line 1, in
<module>
ValueError: invalid literal for int()
with base 10: '100.5‘
2. Entering of values in words
rather than numeric
>>> age=int(input("What is your age
")) What is your age Eighteen

Possible chances of error while
taking input as numbers
3. While input for float value must be compatible. For
e.g. Example 1
>>> percentage=float(input("Enter percentage
")) Enter percentage 12.5.6
File "<stdin>", line 1, in <module>
ValueError: could not convert string to
float: '12.5.6'
Example 2
>>> percentage=float(input("E
nter
percentage ")) Enter percentage 100
percent
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: „100
percent'

Program
1
Open a new script file and type the following
code:
num1=int(input("Enter Number 1
")) num2=int(input("Enter
Number 2 ")) num3 = num1 +
num2
print("Result =",num3)
Save and execute by F5 and

Let us write few
programs
 WAP to enter length and breadth and calculate
area of rectangle
 WAP to enter radius of circle and calculate
area of circle
 WAP to enter Name, marks of 5 subject and
calculate total & percentage of student
 WAP to enter distance in feet and convert it
into inches
 WAP to enter value of temperature in
Fahrenheit and convert it into Celsius.
 WAP to enter radius and height of cylinder
and calculate volume of cylinder.

Operator
s
 are symbol that perform specific operation
when applied on variables. Take a look at the
expression: (Operator)
10 + 25 (Operands) Above
statement is an expression (combination
of operator and operands)
i.e. operator operates on operand. some
operator requires two operand and some requires only
one operand to operate

Types of
Operators
 Unary operators: are those operators that
require one operand to operate upon.
Following are some unary operators:
Operator Purpose
+ Unary plus
- Unary minus
~ Bitwise
complement
Not Logical negation

Types of
Operators
 Binary Operators:are those
operators
that
require two upon.
Following are some Binary
operand to
operate
operators:
1. Arithmetic
Operators
Operator Action
+ Addition
- Subtraction
* Multiplication
/ Division
% Remainder
** Exponent
/ / Floor division

Exampl
e
>>> num1=20
>>> num2=7
>>> val = num1 %
num2
>>>
print(val) 6
>>> val =
2**4
>>>
print(val) 16
>>> val =
num1 /
num2
>>> print(val)
2.85714285714285
7
>>> val = num1 / /

Bitwise
operator
Operator Purpose Action
& Bitwise AND Return 1 if both
inputs are 1
^ Bitwise XOR Return 1, if
the number
of 1 in
input is in
odd
| Bitwise OR Return 1 if
any input is
1
Bitwise operator
works on the binary
value of number not
on the actual value.
For example if 5 is
passed to these
operator it will work
on 101 not on 5.
Binary of
5 is 101, and return
the result in decimal
not in binary.

Exampl
e Binary of 12 is 1100 and 7 is 0111, so applying &
1100
0111
-------
0100 Which is equal to decimal value 4
Guess the output
with
| and ^ ?
Let us see one practical example, T
o check whether entered number is divisible of
2 (or in
a power of 2 or not) like 2, 4, 8, 16, 32 and so on
T
o check this, no need of loop, simply find the bitwise & of n and n-1, if the result
is 0 it means it is in power of 2 otherwise not
Here we can see 0,
it means 32 is in
power of 2
Here we can see
16, it means 24 is
not in power of 2
Later on by using „if‟ we can
print meaningful
message

Identity
Operators
Operators Purpose
<< Shift left
>> Shift right
Operators Purpose
is Is the Identity same?
is not Is the identity not same?

Relational
Operators
Operators Purpose
< Less than
> Greater than
<= Less than or Equal to
>= Greater than or Equal to
== Equal to
!= Not equal to

Logical
Operators
Operators Purpose
and Logical AND
or Logical OR
not Logical NOT

Assignment
Operators
Operators Purpose
= Assignment
/ = Assign quotient
+= Assign sum
-= Assign difference
*= Assign product
**= Assign Exponent
/ / = Assign Floor division

Membership
Operators
Operators Purpose
in Whether variable
in sequence
not in Whether variable not
in sequence

Punctuato
rs
 Punctuators are symbols that are used in
programming languages to organize sentence
structure, and indicate the rhythm and emphasis
of expressions, statements, and program
structure.
 Common punctuators are: „ “ # $ @ []{}=:;(),.

Barebones of Python
Program
 It means basic structure of a Python
program
 Take a look of following code:
#This program shows a program‟s
component # Definition of function
SeeYou() follows
def SeeYou():
print(“This is my function”)
#Main program
A=10
B=A+20
C=A+B
if(C>=100) #checking
condition
print(“Value is equals or more than
100”)
else: print(“Value is less than
100”)
SeeYou()
#Calling
Function
Commen
ts
Functio
n
Stateme
nts
Expressio
ns
Inline
Comment
Bloc
k
Indentatio
n

Expressio
n
 An expression is any legal combination of symbols
that represents a value. An expression is
generally a combination of operators and
operands
Example:
expression of values
only 20, 3.14
Expression that produce a value when
evaluated A+10
Salary * 10 / 100

Statemen
t
 It is a programming instruction that does
something i.e. some action takes place.
 Example
print(“Welcome to python”)
The above statement call print function
When an expression is evaluated a statement is
executed
i.e. some action takes place.
a=100
b = b + 20

Comme
nts
addition
al
informationwritten in
a
 Comments
are program
which
is not executed by interpreter
i.e.
ignored by Interpreter. Comment
contains information regarding statements used,
program flow, etc.
 Comments in Python begins from #
 Python supports 3 ways to enter comments:
1. Full line comment
2. Inline comment
3. Multiline comment

Comme
nts
 Full line comment
Example:
#This is program of volume of
cylinder
 Inline comment
Example # calculating area of
rectangle
area =
length*breadth
 Multiline
comment
Example 1 (using
#)
# Program name: area of
circle # Date: 20/07/18
#Language : Python

Comme
nts
 Multiline comment (using “ “ “) triple
quotes
Example
“ “ “
Program name : swapping of two
number
Date
Logi
c
: 20/07/18
: by using third
variable
FF
F

Function
s
 Function is a block of code that has name and can be
reused by specifying its name in the program
where needed. It is created with def keyword.
Example
def drawline():
print(“======================“)
print(“Welcome to
PythonF) drawline()
print(“Designed by Class
XIF) drawline()

Block and
Indentation
 Group of statement is known as block like
function, conditions or loop etc.
 For e.g.
def area():
a = 10
b = 5
c = a * b
Indentation means extra space before writing any
statement. Generally four space together marks the
next indent level.

Variable
s
 Variables are named temporary location used to
store values which can be further used in calculations,
printing result etc. Every variable must have its own
Identity, type and value. Variable in python is
created by simply assigning value of desired type
to them.
 For e.g
 Num = 100
 Name=“JamesF

Variable
s
 Note: Python variables are not storage containers like
other programming language. Let us analyze by
example.
 In C++, if we declare a variable radius:
radius = 100
[suppose memory address is
41260] Now we again assign new
value to radius
radius = 500
Now the memory address will be still same only
value will change

Variable
s
 Now let us take example of Python:
radius = 100 [memory address 3568]
radius = 700 [memory addres
s 8546]
Now you can see that In python, each time you assign
new value to variable it will not use the same memory
address and new memory will be assigned to variable. In
python the location they refer to changes every time their
value change.(This rule is not for all types of variables)

Lvalues and
Rvalues
 Lvalue : expressionthat comes on the Left
hand Side of Assignment.
 Rvalue : expression that comes on the
Right hand Side of Assignment
Lvalue refers to object to which you can assign value. It refers
to memory location. It can appear LHS or RHS of
assignment
Rvalue refersto the value we assign to any variable.It
can appear on RHS of assignment

Lvalues and
Rvalues
For example (valid use of Lvalue and Rvalue)
x = 100
y = 200
Invalid use of Lvalue and Rvalue
100 = x
200 = y
a+b = c
Note: values cannot comes to the left ofassignment. LHS
must be a
memory location

Multiple
Assignments
 Python is very versatile with assignments. Let‟s see in how
different ways we can use assignment in Python:
1. Assigning same value to multiple variable
a = b = c = 50
2. Assigning multiple values to multiple
variable a,b,c = 11,22,33
Note: While assigningvaluesthrough multiple assignment,remember
that Python first evaluates the RHS and then assigns them to LHS
Examples:

Multiple
Assignments #Statement 1
#Statement 2
x,y,z = 10,20,30
z,y,x = x+1,z+10,y-10
print(x,y,z)
Output will be
10 40 11
Now guess the output of following code
fragment x,y = 7,9
y,z = x-2, x+10
print(x,y,z)

Multiple
Assignments
Let us take another example
y, y = 10, 20
In above code first it will assign 10 to y and again it assign
20 to y, so if you print the value of y it will print 20
Now guess the output of following code
x, x = 100,200
y,y = x + 100, x +200
print(x,y)

Variable
definition
 Variable in python is create when you assign value
to it
i.e. a variable is not create in memory until some
value is assigned to it.
 Let us take as example(if we execute the following
code) print(x)
Python will show an error „x‟ not defined
So to correct the above
code: x=0
print(x)
#now it will show no

Dynamic
Typing
 In Python, a variable declared as numeric type can
be further used to store string type or another.
 Dynamic typing means a variable pointing to a value
of certain type can be made to point to
value/object of different type.
 Lets us understand with example
x = 100
print(x)
x=“KVians
” print(x)
# numeric
type
# now x point to string
type

Dynamic
Typing
x
x=1
0 0
x=“K
Vians”
x
int:
100
int:10
0
string:KVian
s

Caution with Dynamic
Typing
 Always ensure correct operation during dynamic
typing. If types are not used correctly Python may
raise an error
.
Take an
example x =
100
y = 0
y = x / 2
print(y)
x='Exam
'

Determining type of
variable
 Python provides type() function to check
the datatype of variables.
>>> salary=100
>>> type(salary)
<class 'int'>
>>> salary=2000.50
>>> type(salary)
<class 'float'>
>>> name="raka"
>>> type(name)
<class 'str'>

Output through
print()
 Python allows to display output using print().
 Syntax:
print(message_to_print[,sep=“string”,end=“string”]
)
Example 1
print(“Welcom
e”) Example 2
Age=20
print(“Your
age is “, Age)

Output through
print()
Example 3
r = int(input("Enter Radius "))
print("Area of circle is
",3.14*r*r)
Note: from the Example 2 and Example 3 we can
observe that while printing numeric value print()
convert it into equivalent string and print it. In case
of expression (Example 3) it first evaluate it and then
convert the result to string before printing.

Output through
print()
Note:
print() automatically insert space between different values
given in it. The default argument of sep parameter of
print() is space(‘ ‘) .
Example
print(“Name is”,”Vicky”)
Output
Name is Vicky

Output through
print()
Note:
Python allows to change the separator
string.
Example
print(“Name
is”,”Vicky”,”Singh”,sep=“##”)
Output
Name is ##Vicky##Singh

Output through
print()
Note:
Be defaulteach printstatement print the
value to next line. The default value of
end is “ n”
Example
print(“Learning Python”)
print(“Developed by Guido Van
Rossum”) Output
Learning Python
Developed by Guido Van Rossum

Output through
print()
Note:
We can change the value of end to any other
value.
Example
print(“Learning Python”,end=“ “)
print(“Developed by Guido Van
Rossum”) Output
Learning Python Developed by
Guido Van Rossum

Output through
print()
Can you Guess the
output Name=“James”
Salary=20000
Dept=“IT”
print(“Name is
“,Name,end=“@”) print(Dept)
print(“Salary is “,Salary)

Just a
minute…
 What is the difference between keywords
and identifiers
 What are literals in Python? How many
types of literals in python?
 What will be the size of following string
„a‟ , “a” , “Reena‟s”, „”‟, “It‟s”, “XY , “ “
“XY⮠
YZ” YZ”””
 How many types of String in python?

Just a
minute…
 What are the different ways to declare multiline
String?
 Identify the type of following literal:
41.678, 12345, True,„True ,
‟ “False”, 0xCAFE,
0o456,0o971
 Difference between Expression and Statement
 What is the error inn following python program:
print(“Name is “, name)
Suggest a solution

Just a
minute…
 Which of the following string will be the
syntactically correct? State reason.
1. “Welcome to IndiaF
2. „He announced “Start the matchF very loudly‟
3. “Sayonara‟
4. „Revise Python Chapter 1‟
5. “Bonjour
6. “Honesty is the „best‟ policyF

Just a
minute…
 The following code is not giving desired output.
We want to enter value as 100 and obtain
output as 200.
Identify error and correct the program
num = input("enter any
number") double_num =
num * 2
Print("Double
of",num,"is",double_num)

Just a
minute…
 Why the following code is giving
error?
Name="James"
Salary=2000
0 Dept="IT"
print("Name is
",Name,end='@') print(Dept)
print("Salary is ",Salary)

Just a
minute…
 WAP to obtain temperature in Celsius and convert
it into
Fahrenheit.
 What will be the output of
following code: x, y = 6,8
x,y = y, x+2
print(x,y)
 What will be the output of
following code: x,y = 7,2
x,y,x = x+4, y+6,
x+100 print(x,y)

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