Augmented Assignment (Frozen Sets)

00:00 Besides frozen sets being immutable and regular sets being mutable, there’s also another difference. Augmented assignment works differently for normal sets and frozen sets.

00:10 You would think augmented assignment would not work for frozen sets because it mutates regular sets, but it actually does work. Here we see intersection update (&=) and difference update (-=) and symmetric difference update (^=). These all work differently for frozen sets.

00:25 These are actually the same as their expanded out counterparts. So x &= {1} is actually the same as x = x & {1}.

00:37 So, these are actually the same for frozen sets and they’re not the same for regular sets. Here’s our side-by-side comparison. We have x = frozenset({1}), y = x, so now they’re pointing to the same frozenset.

00:52 We use the augmented assignment (|=) to union update x. We print out x, it’s the frozenset({1, 2}). But when we print out y, it’s actually still the frozenset({1}).

01:03 So this reassigned x. Versus y = x, x = x | {2}. This reassigned x to be a new frozenset({1, 2}), and y is still frozenset({1}).

01:18 Something to be careful with when using frozen sets is that you can use this augmented assignment, but you are not mutating it.