Python Basics : Operators

The general purpose of a program is to accept data and perform some operations on the data. The data in the program is stored in variables. The symbol that performs an operation on the data is called an operator.

An operator is a symbol that performs an operation. It acts on some variables called operands. For example, if we write

a + b

the operator '+' is acting on two operands 'a' and 'b'.

If an operator acts on a single variable, its called a unary operator.  If an operator acts on two variables, it is a binary operator etc. We can further classify operators upon their nature as below :

• Arithmetic operators
• Assignment operators
• Unary minus operators
• Relational operators
• Logical operators
• Boolean operators
• Bitwise operators
• Membership operators
• Identity operators

Arithmetic operators

These operators are used to perform basic arithmetic operations like addition, subtraction, division etc. There are seven arithmetic operators available in Python :

1. Addition operator ( a + b ) : Adds two values 'a' and 'b'
2. Subtraction operator ( a - b ) : Subtracts 'b' from 'a'
3. Multiplication operator ( a * b ) : Multiplies two values 'a' and 'b'
4. Division operator ( a / b ) : Divides 'a' by 'b'
5. Modulus operator ( a % b ) : Gives remainder of 'a' by 'b' division
6. Exponent operator ( a ** b ) : Calculates exponential power value of 'a' to the power 'b'
7. Integer division ( a // b ) : Performs division of 'a' by 'b' and gives only integer quotient.

Where there is an expression with several arithmetic operators, the order of evaluation is done based upon operator precedence in the order shown below :

1. Parantheses
2. Exponentiation
3. Muliplication, Division, Modulus and Floor Divisions
4. Addition, Subtraction
5. Assignment operation

Note 1 : The operators with higher precedence will be executed first than of lower precendence.

Note 2 : When evaluating the expression with operators that have the same operator precedence ( for e.g., Multiplication and Division ), the order of evaluation is done from left to right. This is called Associativity. 

Assignment operators

These operators are useful to evaluate the expression on the right side and assign the value to the left side variable. The below are some variations of the assignment operator :

Assignment operator

z = x + y

Stores right side expression value ( i.e., the value of x+y ) into 'z'

Addition assignment operator

z+=x

This expression is similar to z = z + x. Adds 'x' to 'z' and stores the value in 'z'.

Subtraction assignment operator

z-=x

This expression is similar to z = z - x. Subtracts 'x' from 'z' and stores the value in 'z'.

Multiplication assignment operator

z*=x

This expression is similar to  z = z * x. Multiplies 'x' with 'z' and stores the value in 'z'.

Division assignment operator

z/=x

This expression is similar to z = z / x. Divides 'z' by 'x' and stores the value in 'z'.

Modulus assignment operator

z%=x

This expression is similar to z = z % x. Divides 'z' by 'x' and stores the remainder value in 'z'.

Exponentiation assignment operator

z**=x

This expression is similar to z = z ** x. Performs power value and then stores the result into 'z'.

Floor division assignment operator

z//=x

This expression is similar to z = z // x. Performs floor division and then stores the result in 'z'.

Unary Minus Operator

 The unary minus operator is denoted by the symbol minus ( - ) and when this operator is used before a variable, its value is negated.

Relational Operators

Relational operators are used to compare two quantities. The below are the relational operators :

• Greater than operator ( a > b ) : If 'a' is greater than 'b' returns True, else returns False.
• Greater than or equal operator ( a >= b ) : If 'a' is greater than or equal to 'b' returns True, else returns False. 
• Less than operator ( a < b ) : If 'a' is less than 'b' returns True, else returns False.
• Less than or equal operator ( a <= b ) : If 'a' is less than or equal to 'b' returns True, else returns False.
• Equals operator ( a == b ) : if 'a' equals 'b' returns True, else returns False.
• Not equals operator ( a != b ) : if 'a' does not equal 'b' returns True, else returns False.

Relational operators are generally used to construct conditions in if statements.

Logical Operators

Logical operators are useful to construct compound conditions. A compound condition is a combination of more than one simple condition. Each of the simple condition is evaluated to True or False and then the decision is taken to know whether the total condition is True or False. In case of logical operators, False indicates and True indicates any other number.

The below are the logical operators :

• and ( x and y ) : If x is False, x is returned. Else y is returned.
• or ( x or y ) : If x is False, y is returned. Else x is returned.
• not ( not x ) : If x is False, it returns True and vice versa.

Note : When 'and' is used, the total condition will become True only if both conditions are True. When using 'or' if any one condition is True, it will take the total compound condition as True.

Boolean Operators

There are two 'bool' type literals and they are True and False. Boolean operators act upon 'bool' type literals and they provide 'bool' type output.

The below are the boolean operators :

• and ( x and y ) : Boolean and operator
• or ( x or y ) : Boolean or operator
• not ( not x ) : Boolean not operator

Note : Here 'x' and 'y' are boolean values i.e. either True or False.

Bitwise Operators

These operators act on individual bits ( 0 and 1 ) of the operands. The results given by these operators are always in the form of integers.

There are six types of bitwise operators :

• Bitwise Complement operator ( ~ )
• This operator gives the complement form of a given number. 
• The complement form is obtained by changing 0's as 1's and vice versa.
• Bitwise AND operator ( & )
• This operator performs AND operation on the individual bits of numbers.
• By multiplying the input bits, we can obtain the output bits.
• Bitwise OR operator ( | )
• This operator performs OR operation on the individual bits of numbers.
• By adding the input bits, we can obtain the output bits.
• Bitwise XOR operator ( ^ )
• This operator performs XOR operation on the bits on numbers.
• When we have odd number of 1's in the input bits, we can get the output bit as 1.
• Bitwise Left shift operator ( << )
• This operator shifts the bits of the number towards left a specified number of positions.
• If we write x << n, the meaning is to shift the bits of x towards left n positions.
• Bitwise Right shift operator ( >> )
• This operator shifts the bits of the number towards right a specified number of positions.
• If we write x >> n, the meaning is to shift the bits of x towards right n positions.
• Bitwise right shift operator preserves the sign bit, which is the leftmost bit.

Membership Operators

The membership operators are useful to test for membership in a sequence such as strings, lists, tuples or dictionaries. There are two membership operators :

• in : This operator returns True if an element is found in the specified sequence, else False is returned.
• not in : This operator returns True if an element is not found in the sequence, else False is returned.

Identity Operators

These operators compare the memory locations of two objects. The memory location of an object can be seen using the id() function. This function returns an integer number, called the identity number that internally represents the memory location of the object. In Python, everything is considered an object. There are two identity operator :

• is : The 'is' operator is useful to compare whether two objects are same or not by internally comparing the identity number of the objects. If they are same, True is returned. Else, False is returned.
• is not : The 'is not' operator returns True if the identity numbers of two objects being compared are not same. Else False is returned.