Operators

Objectives

• Understand the use and application of the assignment operator
• Use mathematical operators (+, -, *, /, %, //) for simple calculations
• Learn how to use the augmented assignment operators
• Be able to construct expressions, applying operator precedence
• Understand and use logical operators (and, or, not) in Python.
• Understand the role and use of comparison Operators (==, !=, >, <, >=, <=)
• Build expressions combining logical and comparison operators
• Apply parentheses to modify the evaluation order of logical expressions.

In this section we will look at the different operators we can use when programming with Python. An operator is a character, or characters that will carry out a function on its operands.

The concept will be familiar from using basic arithmetic operators such as + or - to add two numbers together or subtract two numbers. The + is known as an operator, and the numbers being added are the operands.

Programming languages have a number of types of operators:

• Mathematical operators
• comparison operators
• logical operators

One other is the assignment operator (=) that we used in the previous section.

Example 2

Review the following program:

a = 10
b = 5
result = a + b * 2
print("Result 1:", result)

result = (a + b) * 2
print("Result 2:", result)

result = a // b
print("Result 3:", result)

is_greater = a > b
print("Is a greater than b?", is_greater)

logical_test = (a > b) and (a < 20)
print("Logical test:", logical_test)

Here there are a number of these operators being used. Read the code and predict what will be printed to the screen when the highlighted lines are executed.

Answers

• Result 1: 20
• Result 2: 30
• Result 3: 2
• Is a greater than b? True
• Logical test: True

Copy the code and paste into a code editor and run the code to compare your predictions with the actual results.

Compare lines 4 and lines 7. Why is the result different?

The following sections summarise the behaviour of each type of operator that we use when programming.

Assignment Operator

We've already seen this being used. It is the equals sign, =, but as we noted before we read it as "is assigned to".

We can practice its use with the interactive environment:

>>> name = "Simon"
>>> age = 42

When reading this code say: "Simon is as assigned to the variable name" and "42 is assigned to the variable age". The computer will then store this value in its memory and they can then be referred to by using their name, or identifier:

>>> print(name, age)
Simon 42

Mathematical operators

The mathematical operators are the same we have in maths, noting the use of / for division and * for multiplication:

• Addition: +
• Subtraction: -
• Division: /
• Multiplication: *

Operator	Description	Example	Result
+	Addition	7 + 3	10
-	Subtraction	7 - 3	4
-	Multiplication	7 * 3	21
/	Division	7 / 3	2.33333..

Note

When two integers are divided, the result is a real (floating point number)

There is also a pair of integer division operators:

Operator	Description	Example	Result
//	Floor division	7 // 3	2
%	Modulo (Remainder)	7 % 3	1

Try both of these in the interactive environment to confirm results.

If we think of an example of wanting to know how many hours and minutes for a movie that lasts 138 minutes. We can get the hours by using the integer division operator: hours = minutes // 60. This automatically rounds down. We can get the remainder too: remainder = minutes - (hours * 60). But this is the same as using the modulo operator: remainder = minutes % 60.

The modulo operator is also really useful when checking if one divides equally into another. For example: if x % 2 == 0, then we know if the number (x) is odd or even.

Finally, exponent operator, **:

Operator	Description	Example	Result
**	Exponent	7 ** 3	343

Augmented assignment operators

The following expression is often used where the value of a variable is being incremented by a given amount:

x = x + 1

Here we can use a shorthand form (sometimes called syntactic sugar):

x += 1              # the same as x = x + 1

Any of the mathematical operators can be used in this way.

# Initial assignment
x = 10
print(x)            # output: 10

# Augmented assignment operator: subtraction
x -= 2
print(x)            # output: 8

# Augmented assignment operator: multiplication
x *= 3  
print(x)            # output: 24

It does not matter which you prefer to use but the shorter form takes a little less typing.

Note

This is sometimes known as an in-place operator

Operator precedence

There should be no surprises here, at least initially:

• exponentiation
• multiplication or division
• addition or subtraction

As in maths any brackets take priority, so these can be used to alter the order of precedence

Comparison operators

Comparison operators in Python are used to compare two values or expressions and produce Boolean results (True or False). These operators allow you to check conditions and make decisions based on the results of these comparisons. They are usually used as part of selection and iteration structures which we'll meet later.

Python provides several comparison operators:

Operator	Description	Example	Result
==	Equal to	7 == 7	True
!=	Not Equal to	7 != 6	True
>	Greater than	7 > 6	True
<	Less than	7 < 6	False
>=	Greater than or equal to	7 >= 7	True
<=	Less than or equal to	7 <= 7	True

Warning

Pay attention to the "is equal to" operator ( == ), it's two equal signs. It’s easy to mistake it for the assignment operator ( = ). It helps to read the assignment operator as e.g. "age is assigned the value 18" for age = 18; and "is age equal to 18" for age == 18.

Logical operators

Logical operators in Python allow us to combine logical operations on one or more Boolean values (True or False). These operators are used to make decisions and control the flow of a program based on those conditions. They are often referred to as Boolean operators.

Python provides three main logical operators:

Operator	Description	Example	Result
and	Returns True only if all the boolean values are true	(7 > 6) and (4 < 8)	True
or	Returns True if at least one of the boolean values are true	(10 < 20) or (10 < 5)	True
not	Returns True if the value is false; returns `False if the value is true	not(7 > 6)	False

Logical Operator Examples

Let's explore these logical operators with some examples, you can try these in the interactive environment:

1. AND Operator (and)

The and operator returns True only if both conditions are True.

>>> x = True
>>> y = False
>>> x and y
False

2. OR Operator (or)

The or operator returns True if at least one condition is True.

>>> a = True
>>> b = False
>>> a or b
True

3. NOT Operator (not)

The not operator negates the Boolean value.

>>> p = True
>>> not p
False

Combining Logical Operators

You can combine logical operators to create more complex conditions:

age = 25
is_student = False

if age >= 18 and not is_student:
    print("You are eligible to vote.")
else:
    print("You are not eligible to vote.")

You are eligible to vote.

In this example, the and operator is used to check if the age is greater than or equal to 18, and the not operator is used to check if the person is not a student.

Precedence of Logical Operators

Logical operators have a specific order of precedence: not has the highest precedence, followed by and, and then or. You can use parentheses to change the order of evaluation if needed.

result = (True or False) and (not True)

Common Use Cases

Logical operators are commonly used in programming for various purposes, such as:

• Conditional Statements: To make decisions and control the flow of a program using if, elif, and else statements.
• Loop Control: To control the execution of loops, such as while and for loops.
• Filtering Data: To filter data based on specific conditions.
• Searching and Validation: To search for specific values in data and validate user input.

Climate Quest Project

Throughout this topic we'll be working on a large scale project: Climate Quest. In this project a player embarks on a journey to combat the effects of climate change by making decisions that impact the environment. Each choice affects the outcome of the game, emphasizing the importance of individual actions in addressing climate change.

Go to task 2 - Using Operators

Questions

1. What is the purpose of an operator in computer science?

To represent a specific operation to be performed on one or more operands.

To assign values to variables.

To control the flow of a program.

To filter data based on specific conditions.

An operator in computer science is a symbol or keyword that specifies an operation to be performed on one or more operands (e.g., variables or values). For example, the + operator is used to add two numbers.

Submit

2. Which of the following operators is used to assign values to variables in Python?

==

=

+

/

The = operator in Python is used to assign a value to a variable. For instance, x = 5 assigns the value 5 to the variable x. It is important to note that = is not the same as ==, which is used for comparison.

Submit

3. What is the result of the expression 7 // 2 in Python?

3.5

3

4

3.0

The // operator in Python performs integer (or floor) division, which returns the largest integer less than or equal to the result of the division. Therefore, 7 // 2 results in 3, discarding the fractional part.

Submit

4. Which operator is used for exponentiation in Python?

^

%

//

**

The ** operator is used in Python to perform exponentiation, which raises a number to the power of another number. For example, 2 ** 3 results in 8 (2 raised to the power of 3).

Submit

5. What does the += operator do in Python?

Subtracts a value from a variable.

Multiplies a variable by a value.

Adds a value to a variable.

Divides a variable by a value.

The += operator in Python is an example of an augmented assignment operator. It adds the value on the right to the variable on the left and then assigns the result back to that variable. For instance, x += 3 is equivalent to x = x + 3.

Submit

6. Which comparison operator checks if two values are not equal in Python?

==

>=

<

!=

The != operator in Python checks whether two values are not equal. If the values are not equal, it returns True; otherwise, it returns False. For example, 5 != 3 returns True.

Submit

7. What is the order of precedence for mathematical operations in Python?

Exponentiation, Addition/Subtraction, Multiplication/Division

Multiplication/Division, Addition/Subtraction, Exponentiation

Addition/Subtraction, Exponentiation, Multiplication/Division

Exponentiation, Multiplication/Division, Addition/Subtraction

In Python, the order of precedence for mathematical operations follows standard mathematical rules: exponentiation (**) is performed first, followed by multiplication and division (*, /, //, %), and finally addition and subtraction (+, -).

Submit

8. Which logical operator returns True only if both conditions are True?

and

or

not

==

The and operator in Python returns True only if both conditions it is evaluating are True. If either condition is False, the result is False. For example, True and False returns False.

Submit

9. What is the purpose of using parentheses, (brackets), in logical expressions?

To change the order of evaluation.

To combine multiple expressions.

To separate operands.

To indicate comments.

Parentheses in logical expressions are used to alter the natural order of evaluation, ensuring that the expressions inside the parentheses are evaluated first. This is similar to their use in mathematical expressions.

Submit

10. What is the result of the expression not True?

False

True

null

Error

The not operator in Python negates a boolean value. If applied to True, it returns False, and if applied to False, it returns True. Therefore, not True results in False.

Submit

Programming Tasks

For each of the following tasks write a program using Python.

Exponentiation

Write Python code to calculate the result of 2^5 (2 raised to the power of 5) using the exponentiation operator.

Read more ...

Odd or Even

Create a Python program that asks the user to input a number and then checks whether the number is odd or even. The program should display a message indicating whether the number is odd or even. The expected output is:

Read more ...

Integer division

Implement a Python program that calculates the quotient and remainder when dividing 23 by 5 without using the `/` operator. Use the integer division operator `//` and the modulo operator `%`

Read more ...

BMI Calculator

Develop a Python program that calculates the Body Mass Index (BMI) of a person based on their weight and height. The program should prompt the user to input their weight (in kilograms) and height (in meters), calculate their BMI using the BMI formula `bmi = weight_kg / (height_m ** 2)`, and then display the result.

Read more ...