Introduction

• In this chapter we will learn data types, variables, operators and expression in detail.
• Python has a predefined set of data types to handle the data in a program.
• We can store any type of data in Python.

DATA TYPES

• Data can be of any type like- character, integer, real, string.
• Anything enclosed in “ “ is considered as string in Python.
• Any whole value is an integer value.
• Any value with fraction part is a real value.
• True or False value specifies boolean value.
• Python supports following core data types-

I.	Numbers	(int like10, 5) (float like 3.5, 302.24) (complex like 3+5i)
II.	String	(like “pankaj”, ‘pankaj’, ‘a’, “a” )
III.	List	like [3,4,5,”pankaj”] its elements are Mutable.
IV.	Tuple	like(3,4,5,”pankaj”) its elements are immutable.
V.	Dictionary	like {‘a’:1, ‘e’:2, ‘I’:3, ‘o’:4, ‘u’:5} where a,e,i,o,u are keys and 1,2,3,4,5 are their values.

CORE DATA TYPES

Mutable and Immutable Types

In Python, Data Objects are categorized in two types-
      * Mutable (Changeable)
      * Immutable (Non-Changeable)

Look at following statements carefully-

Now, try to change the values-

Answer is NO.
Because here values are objects and p, q, r are their reference name.
To understand it, lets see the next slide.

Variables and Values

An important fact to know is-
–In Python, values are actually objects.
–And their variable names are actually their reference names.

Suppose we assign 10 to a variable A.
A = 10
Here, value 10 is an object and A is its reference name.

If we assign 10 to a variable B, B will refer to same object.
Here, we have two variables, but with same location.

Now, if we change value of B like B=20

Then a new object will be created with a new location 20 and this object will be referenced by B.

Mutable and Immutable Types

Following data types comes under mutable and immutable types-

Mutable (Changeable)
     –lists, dictionaries and sets.

Immutable (Non-Changeable)
     –integers, floats, Booleans, strings and tuples.

Variable Internals

The Type of an Object

Pay attention to the following command-

The Value of an Object

The ID of an Object

Operators

• The symbols that shows a special behavior or action when applied to operands are called operators. For ex- + , – , > , < etc.

• Python supports following operators-
       I. Arithmetic Operator
       II. Relation Operator
       III. Identity Operators
       IV. Logical Operators
       V. Bitwise Operators
       VI. Membership Operators

Arithmetic Operators

For addition +      ——–>       for ex- 2+3 will result in to 5
For subtraction –      ——–>       for ex- 2-3 will result in to -1
For multiplication *      ——–>     for ex- 2*3 will result in to 6  
For division /      ——–>       its result comes in fraction. for ex- 13/2 will result in to 6.5
For quotient //      ——–>       its result comes as a whole number for ex- 13/2 will result into 6.
For remnant %      ——–>       its result comes as a whole remnant number.For ex-13/2 will result into 1.
For exponent **      ——–>       it will come as per exponent value. For ex- 2³ will result into 8.

Assignment Operators and short hand

Python has following assignment operator and shorthand –

=           a=10 , 10 will be assigned to a.
+=        a+=5 is equal to a=a+5.
-=         a-=5 is equal to a=a-5.
*=         a*=5 is equal to a=a*5.
/=         a/=5 is equal to a=a/5.
//=         a//=5 is equal to a=a//5.
%=        a%=5 is equal to a=a%5.
**=        a**=5 is equal to a=a**5.

Relational Operators

Python uses Relational operators to check for equality. These results into true or false. Relational Operator are of following types-

<	Less Than	like a<b
>	Greater Than	like a>b
<=	Less Than and Equal to	like a<=b
>=	Greater Than and Equal to	like a>=b
==	Equal to	like a==b
!=	not Equal to	like a!=b

Identity Operators

Identity operator is also used to check for equality. These expression also results into True or False. Identity Operators are of following types-

Identity operator is also used to check for equality. These expression also results into True or False. Identity Operators are of following types-

      • “is” operator                   if a=5 and b=5 then a is b will come to True
      • “is not” operator              if a=5 and b=5 then a is not b will come to False

Relational Operator ( == ) and Identity operator (is) differs in case of strings that we will see later.

Logical Operators

• Python has two binary logical operators –
         or operator
                »if a = True and b = False then a or b will return True.
         and operator
                »If a = True and b = False then a and b will return False.

• Python has one Unary logical operator –
         not operator
                if a = True then not a will return False.

Operator Associativity

• In Python, if an expression or statement consists of multiple or more than one operator then operator associativity will be followed from left-to-right.

• In above given expression, first 7*8 will be calculated as 56, then 56 will be divided by 5 and will result into 11.2, then 11.2 again divided by 2 and will result into 5.0.

*Only in case of **, associativity will be followed from right-to-left.

Above given example will be calculated as 3**(3**2).

Expressions

Python has following types of expression –

• Arithmetic Expressions like a+b, 5-4 etc.
• Relational Expressions like a>b, a==b etc.
• Logical Expressions like a>b and a>c , a or b etc.
• String Expressions like “Pankaj” + “Kumar” etc.

Type Casting

• As we know, in Python, an expression may be consists of mixed datatypes. In such cases, python changes data types of operands internally. This process of internal data type conversion is called implicit type conversion.

• One other option is explicit type conversion which is like-
          <datatype> (identifier)
  For ex-
          a=“4”
          b=int(a)
  Another ex-
          If a=5 and b=10.5 then we can convert a to float.
          Like d=float(a)
  In python, following are the data conversion functions-
  (1) int( )   (2) float( )   (3) complex( )   (4) str( )   (5) bool( )

Working with math Module of Python

Python provides math module to work for all mathematical works. We need to write following statement in our program-

Taking Input in Python

In Python, input () function is used to take input which takes input in the form of string. Then it will be type casted as per requirement. For ex- to calculate volume of a cylinder, program will be as-

Its output will be as-