Python: Essential Reference, Third Edition

Augmented Assignment

Python provides the following set of augmented assignment operators:

Operation	Description
x += y	x = x + y
x -= y	x = x - y
x *= y	x = x * y
x /= y	x = x / y
x //= y	x = x // y
x **= y	x = x ** y
x %= y	x = x % y
x &= y	x = x & y
x |= y	x = x | y
x ^= y	x = x ^ y
x >>= y	x = x >> y
x <<= y	x = x << y

These operators can be used anywhere that ordinary assignment is used. For example:

a = 3
b = [1,2]
c = "Hello %s %s"
a += 1                      # a = 4
b[1] += 10                  # b = [1, 12]
c %= ("Monty", "Python")    # c = "Hello Monty Python"

Augmented assignment doesn’t violate mutability or perform in-place modification of objects. Therefore, writing x += y creates an entirely new object x with the value x + y. User-defined classes can redefine the augmented assignment operators ...