What Do +=, -= Mean?

Operators like +=, -=, which combine an operator with an = sign, are called Compound Assignment Operators.

For instance, x += y means the same as x = x + y, where the value of x is updated by adding y to x.

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x = 10
y = 5

x += y  # x = x + y
print(x)  # 15

In Python, compound assignment operators include += (addition), -= (subtraction), *= (multiplication), /= (division), %= (modulus), and others.

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number = 10
print("number:", number)  # 10

number += 5  # number = number + 5

print("number += 5:", number)  # 15


number -= 3  # number = number - 3

print("number -= 3:", number)  # 12


number *= 2  # number = number * 2

print("number *= 2:", number)  # 24


number /= 4  # number = number / 4

print("number /= 4:", number)  # 6.0


number %= 2  # number = number % 2

print("number %= 2:", number)  # 0.0

Compound assignment operators are often used in loops, such as when adding numbers from 1 to 5.

Note: For more details about loops, refer to the lesson How to Perform Repetitive Tasks in Python Based on Conditions.

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numbers = [1, 2, 3, 4, 5]

total = 0

for num in numbers:
    total += num

print("total:", total)  # 15