4.2 Assignment operators

4.2a What are assignment operators?

Assignment operators in Python are used to change the value of a variable. They combine a basic math operation (like addition or multiplication) with assigning a new value to the variable. They make your code shorter and easier to read.

4.2b Why use these assignment operators?

• Convenience - They make your code shorter and easier to write.
• Readability - They make it clear that you are updating the value of a variable.

4.2c Main assignment operators

The main assignment operators that we will use in this course are:

+= (Add and Assign)

This operator adds a number to the current value of a variable and then assigns the new value to that variable.

Example 4.2.1

x = 5
x += 3  # This is the same as x = x + 3
print(x)

8

-= (Subtract and Assign)

This operator subtracts a number from the current value of a variable and then assigns the new value to that variable.

Example 4.2.2

x = 5
x -= 2  # This is the same as x = x - 2
print(x)

Example 4.2.2 - Output

3

*= (Multiply and Assign)

This operator multiplies the current value of a variable by a number and then assigns the new value to that variable.

Example 4.2.3

x = 5
x *= 4  # This is the same as x = x * 4
print(x)

Example 4.2.3 - Output

20

/= (Divide and Assign)

This operator divides the current value of a variable by a number and then assigns the new value to that variable.

Example 4.2.4

x = 10
x /= 2  # This is the same as x = x / 2
print(x) 

Example 4.2.4 - Output

5.0
# Note the decimal

//= (Floor Divide and Assign)

This operator divides the current value of a variable by a number, rounds down to the nearest whole number, and then assigns the new value to that variable.

Example 4.2.5

x = 10
x //= 3  # This is the same as x = x // 3
print(x)

Example 4.2.5 - Output

3

%= (Modulus and Assign)

This operator calculates the remainder when the current value of a variable is divided by a number and then assigns the new value (the remainder) to that variable.

Example 4.2.6

x = 10
x %= 3  # This is the same as x = x % 3
print(x)

Example 4.2.6 - Output

1

4.2d Interpret a program snippet that includes assignment operators.

Example 4.2.7 - In this example, you can see how each assignment operator changes the value of x step by step.

x = 10  # Start with x equal to 10

x += 5  # Add 5 to x, now x is 15
x -= 3  # Subtract 3 from x, now x is 12
x *= 2  # Multiply x by 2, now x is 24
x /= 4  # Divide x by 4, now x is 6.0
x //= 2  # Floor divide x by 2, now x is 3
x %= 2  # Get the remainder of x divided by 2, now x is 1

print(x)

Example 4.2.7 - Output

1.0

4.2e Develop a program using assignment operators.

Exercise 4.2.1 - Write a Python program that starts with a variable score set to 100. Perform the following operations on score using assignment operators and print the result after each operation:

• Decrease score by 15 using -=.
• Increase score by 20 using +=.
• Multiply score by 3 using *=.
• Divide score by 2 using /=.
• Floor divide score by 5 using //=.
• Take the remainder of score divided by 4 using %=.

_{Exercise 4.2.1 - Model Answer - Make sure to work out the exercise before checking the model answer.}