Chapter 4: Making Python Work - Operators

In Chapter 3, you learned how to store information in variables. Now it's time to learn how to do things with that information. Whether you want to perform calculations, compare values, or combine text, you'll need to use operators.

Operators are special symbols in Python that carry out an operation on one or more values (called operands). For example, in the expression 10 + 5, 10 and 5 are the operands, and + is the addition operator.

Let's explore the most common types of operators you'll be using.

Arithmetic Operators

These are the operators you're likely most familiar with from math class. They let you perform mathematical calculations. Let's assume we have two variables for our examples: a = 15 and b = 4.

Operator	Name	Description	Example	Result
+	Addition	Adds two operands	a + b	19
-	Subtraction	Subtracts the right operand from the left operand	a - b	11
*	Multiplication	Multiplies two operands	a * b	60
/	Division	Divides the left operand by the right. The result is always a float.	a / b	3.75
%	Modulus	Returns the remainder of the division	a % b	3
**	Exponentiation	Raises the left operand to the power of the right operand	a ** b	50625
//	Floor Division	Divides and returns the whole number result (rounds down).	a // b	3

Here are these operators in action in a Python script:

a = 15
b = 4

# Basic arithmetic
print("a + b =", a + b)
print("a - b =", a - b)
print("a * b =", a * b)

# Division
print("a / b =", a / b)             # Classic division (always a float)
print("a // b =", a // b)           # Floor division (result is an integer)
print("a % b =", a % b)             # Modulus (the remainder)

# Exponentiation (a to the power of b)
print("a ** b =", a ** b)

Order of Operations Python follows the standard mathematical order of operations, often remembered by the acronym PEMDAS:

1. Parentheses ()

2. Exponents *

3. Multiplication , Division /, Floor Division //, Modulus % (from left to right)

4. Addition +, Subtraction (from left to right)

result = 5 + 2 * 3   # Multiplication is done first: 5 + 6
print(result)        # Output: 11

result_with_parens = (5 + 2) * 3  # Parentheses are done first: 7 * 3
print(result_with_parens)      # Output: 21

Assignment Operators

You've already used the most basic assignment operator, =. Assignment operators are used to assign values to variables. There are also "compound" assignment operators that combine an arithmetic operation with an assignment.

Let's start with a variable x = 10.

Operator	Example	Equivalent to...	Description
=	x = 10	x = 10	Assigns the value on the right to the variable on the left.
+=	x += 5	x = x + 5	Adds the right value to the variable and reassigns the result.
-=	x -= 5	x = x - 5	Subtracts the right value and reassigns.
*=	x *= 5	x = x * 5	Multiplies by the right value and reassigns.
/=	x /= 5	x = x / 5	Divides by the right value and reassigns.
%=	x %= 3	x = x % 3	Performs modulus and reassigns the remainder.
//=	x //= 3	x = x // 3	Performs floor division and reassigns.
**=	x **= 2	x = x ** 2	Raises to a power and reassigns.

These are useful shortcuts that make your code cleaner and more concise.

score = 100

# The player gains 25 points
score += 25  # same as score = score + 25
print(score) # Output: 125

# The player loses 10 points
score -= 10  # same as score = score - 10
print(score) # Output: 115

Comparison Operators

Comparison operators are used to compare two values. The result of a comparison is always a Boolean value: True or False. These are essential for making decisions in your code.

Let's use x = 10 and y = 12 for our examples.

Operator	Name	Example	Result	Description
==	Equal to	x == y	False	Returns True if the operands are equal.
!=	Not equal to	x != y	True	Returns True if the operands are not equal.
>	Greater than	x > y	False	Returns True if the left operand is greater.
<	Less than	x < y	True	Returns True if the left operand is smaller.
>=	Greater than or equal to	x >= y	False	Returns True if the left is greater or equal.
<=	Less than or equal to	x <= y	True	Returns True if the left is smaller or equal.

Important: Don't confuse the assignment operator (=) with the "equal to" comparison operator (==).

• my_variable = 5 assigns the value 5 to my_variable.

• my_variable == 5 checks if my_variable is equal to 5 and returns True or False.

age = 20
voting_age = 18

can_vote = age >= voting_age
print("Can this person vote?", can_vote) # Output: Can this person vote? True

Logical Operators

Logical operators are used to combine Boolean expressions. They allow you to test multiple conditions at once.

Operator	Description	Example	Result
and	Returns True if both statements are true.	(5 > 3) and (2 < 4)	True
or	Returns True if at least one of the statements is true.	(5 > 3) or (2 > 4)	True
not	Reverses the result; returns False if the result is true, and vice-versa.	not(5 > 3)	False

Logical operators are incredibly powerful when you need to make more complex decisions.

age = 25
has_license = True

# Check if a person is old enough to rent a car AND has a license
can_rent_car = (age >= 25) and (has_license == True)
print("Can rent a car:", can_rent_car) # Output: Can rent a car: True

is_weekend = False
is_holiday = True

# Check if you can sleep in (if it's a weekend OR a holiday)
can_sleep_in = is_weekend or is_holiday
print("Can sleep in:", can_sleep_in) # Output: Can sleep in: True

Summary and What's Next

You've just learned a crucial part of programming: how to use operators to manipulate and compare data.

• Arithmetic Operators (+, , , /, %, *, //) for calculations.

• Assignment Operators (=, +=, =, etc.) for assigning and updating values.

• Comparison Operators (==, !=, >, <, etc.) for comparing values to get a True or False result.

• Logical Operators (and, or, not) for combining True/False conditions.

These tools are the building blocks for creating logic in your programs. Now that you can store data (variables) and compare it (operators), you're ready for the next giant leap: Control Flow. In the next chapter, you'll learn how to make your programs make decisions and run different pieces of code based on the conditions you've learned to create here.

Practice Time!

1. Predict the output of 10 + 3 * 2 ** 2. Then, type it into a Python shell to check your answer.

2. Create a variable temp_celsius = 25. Write a formula using an arithmetic operator to convert it to Fahrenheit and print the result. (Formula: F = C * 9/5 + 32).

3. Create two variables, password = "secret" and username = "admin". Write a comparison to check if the password variable is equal to "secret". Print the True/False result.

4. Write a logical expression that checks if a student has passed. A student passes if their grade is 80 or higher and they have completed_homework. Create variables for grade and completed_homework to test it.