Python a &= b meaning?

Question

What does the &= operator mean in Python, and can you give me a working example?

I am trying to understand the __iand__ operator.

I just d

Answer 1

Contrary to some of the other answers, a &= b is not shorthand for a = a & b, though I admit it often behaves similarly for built-in immutable types like integers.

a &= b can call the special method __iand__ if available. To see the difference, let's define a custom class:

class NewIand(object):
    def __init__(self, x):
        self.x = x
    def __and__(self, other):
        return self.x & other.x
    def __iand__(self, other):
        return 99  

After which we have

>>> a = NewIand(1+2+4)
>>> b = NewIand(4+8+16)
>>> a & b
4
>>> a = a & b
>>> a
4

but

>>> a = NewIand(1+2+4)
>>> b = NewIand(4+8+16)
>>> a &= b
>>> a
99