• cattrs version: 1.2.0
• Python version: 3.7.9
• Operating System: Linux

Description

There are a few spots in the code where I unstructure a tuple of attrs objects in preparation for JSON-encoding them. This stopped working with 1.2.0.

What I Did

Here's a minimal reproducer:

#!/usr/bin/env python3

import attr
import cattr

@attr.define()
class Foo:
    foo: str

assert cattr.unstructure((Foo("foo"),)) == ({"foo": "foo"},)

I've bisected this to 53fd2ad. From looking at that commit quickly, I'm guessing that switching from _subclass(Sequence) to is_sequence is causing a tuple to no longer be considered a sequence.