# Operators and expressions¶

In Python most of the lines you will write will be expressions. Expressions are made of operators and operands. An expression is like 2 + 3 .

## Operators¶

Operators are the symbols which tells the Python interpreter to do some mathematical or logical operation. Few basic examples of mathematical operators are given below:

```>>> 2 + 3
5
>>> 23 - 3
20
>>> 22.0 / 12
1.8333333333333333
```

To get floating result you need to the division using any of operand as floating number. To do modulo operation use % operator

```>>> 14 % 3
2
```

## Example of integer arithmetic¶

The code

```#!/usr/bin/env python3
days = int(input("Enter days: "))
months = days / 30
days = days % 30
print("Months = %d Days = %d" % (months, days))
```

The output

```\$ ./integer.py
Enter days: 265
Months = 8 Days = 25
```

In the first line I am taking the input of days, then getting the months and days and at last printing them. You can do it in a easy way

```#!/usr/bin/env python3
days = int(input("Enter days: "))
print("Months = %d Days = %d" % (divmod(days, 30)))
```

The divmod(num1, num2) function returns two values , first is the division of num1 and num2 and in second the modulo of num1 and num2.

## Relational Operators¶

You can use the following operators as relational operators

### Relational Operators¶

 Operator Meaning < Is less than <= Is less than or equal to > Is greater than >= Is greater than or equal to == Is equal to != Is not equal to

Some examples

```>>> 1 < 2
True
>>> 3 > 34
False
>>> 23 == 45
False
>>> 34 != 323
True
```

// operator gives the floor division result

```>>> 4.0 // 3
1.0
>>> 4.0 / 3
1.3333333333333333
```

## Logical Operators¶

To do logical AND , OR we use and ,*or* keywords. x and y returns False if x is False else it returns evaluation of y. If x is True, it returns True.

```>>> 1 and 4
4
>>> 1 or 4
1
>>> -1 or 4
-1
>>> 0 or 4
4
```

## Shorthand Operator¶

x op = expression is the syntax for shorthand operators. It will be evaluated like x = x op expression , Few examples are

```>>> a = 12
>>> a += 13
>>> a
25
>>> a /= 3
>>> a
8.333333333333334
>>> a += (26 * 32)
>>> a
840.3333333333334
```

shorthand.py example

```#!/usr/bin/env python3
N = 100
a = 2
while a < N:
print("%d" % a)
a *= a
```

The output

```\$ ./shorthand.py
2
4
16
```

## Expressions¶

Generally while writing expressions we put spaces before and after every operator so that the code becomes clearer to read, like

```a = 234 * (45 - 56.0 / 34)
```

One example code used to show expressions

```#!/usr/bin/env python3
a = 9
b = 12
c = 3
x = a - b / 3 + c * 2 - 1
y = a - b / (3 + c) * (2 - 1)
z = a - (b / (3 + c) * 2) - 1
print("X = ", x)
print("Y = ", y)
print("Z = ", z)
```

The output

```\$ ./evaluationexp.py
X =  10
Y =  7
Z =  4
```

At first x is being calculated. The steps are like this

```9 - 12 / 3 + 3 * 2 -1
9 - 4 + 3 * 2 - 1
9 - 4 + 6 - 1
5 + 6 - 1
11 - 1
10
```

Now for y and z we have parentheses, so the expressions evaluated in different way. Do the calculation yourself to check them.

## Type Conversions¶

We have to do the type conversions manually. Like

```float(string) -> float value
int(string) -> integer value
str(integer) or str(float) -> string representation
>>> a = 8.126768
>>> str(a)
'8.126768'
```

## evaluateequ.py¶

This is a program to evaluate 1/x+1/(x+1)+1/(x+2)+ … +1/n series upto n, in our case x = 1 and n =10

```#!/usr/bin/env python3
sum = 0.0
for i in range(1, 11):
sum += 1.0 / i
print("%2d %6.4f" % (i , sum))
```

The output

```\$ ./evaluateequ.py
1 1.0000
2 1.5000
3 1.8333
4 2.0833
5 2.2833
6 2.4500
7 2.5929
8 2.7179
9 2.8290
10 2.9290
```

In the line sum += 1.0 / i what is actually happening is sum = sum + 1.0 / i.

This is a program to evaluate the quadratic equation

```#!/usr/bin/env python3
import math
a = int(input("Enter value of a: "))
b = int(input("Enter value of b: "))
c = int(input("Enter value of c: "))
d = b * b - 4 * a * c
if d < 0:
print("ROOTS are imaginary")
else:
root1 = (-b + math.sqrt(d)) / (2.0 * a)
root2 = (-b - math.sqrt(d)) / (2.0 * a)
print("Root 1 = ", root1)
print("Root 2 = ", root2)
```

## salesmansalary.py¶

In this example we are going to calculate the salary of a camera salesman. His basic salary is 1500, for every camera he will sell he will get 200 and the commission on the month’s sale is 2 %. The input will be number of cameras sold and total price of the cameras.

```#!/usr/bin/env python3
basic_salary = 1500
bonus_rate = 200
commision_rate = 0.02
numberofcamera = int(input("Enter the number of inputs sold: "))
price = float(input("Enter the total prices: "))
bonus = (bonus_rate * numberofcamera)
commision = (commision_rate * numberofcamera * price)
print("Bonus        = %6.2f" % bonus)
print("Commision    = %6.2f" % commision)
print("Gross salary = %6.2f" % (basic_salary + bonus + commision))
```

The output

```\$ ./salesmansalary.py
Enter the number of inputs sold: 5
Enter the total prices: 20450
Bonus        = 1000.00
Commision    = 2045.00
Gross salary = 4545.00
```