Serhiy Storchaka added the comment:
It is okay. In this case `a |= b` is equivalent to `a = a | b`.
The same behavior is for tuples, strings, and other non-mutable collections:
t = (1, 2)
t += (3, 4)
s = 'ab'
s += 'cd'
And even for numbers!
i = 5
i += 1
--
nosy: +serhiy.storchaka
r
New submission from Chris Cordero :
Frozensets disallow the .update and the .__ior__ methods from being used, but
allows the |= operator, which I think is inconsistent with the disallowed
methods†.
```
foo = frozenset()
print(foo) # frozenset()
foo.update({"hello"}) # AttributeErr
