$ cat author.py 
class xxxxxxxxxxxxxxxxxxxxx(xxxx.xxxxxxxxxxxxx):
    def xxxxxxx_xxxxxx(xxxx):
        assert xxxxxxx_xxxx in [
            x.xxxxx.xxxxxx.xxxxx.xxxxxx,
            x.xxxxx.xxxxxx.xxxxx.xxxx,
        ], ("xxxxxxxxxxx xxxxxxx xxxx (xxxxxx xxxx) %x xxx xxxxx" % xxxxxxx_xxxx)
$ black -v author.py 
Using configuration from /Users/jelle/py/black/pyproject.toml.
Traceback (most recent call last):
  File "/Users/jelle/py/black/src/black/__init__.py", line 648, in reformat_one
    if changed is not Changed.CACHED and format_file_in_place(
  File "/Users/jelle/py/black/src/black/__init__.py", line 791, in format_file_in_place
    dst_contents = format_file_contents(src_contents, fast=fast, mode=mode)
  File "/Users/jelle/py/black/src/black/__init__.py", line 912, in format_file_contents
    dst_contents = format_str(src_contents, mode=mode)
  File "/Users/jelle/py/black/src/black/__init__.py", line 977, in format_str
    for line in transform_line(
  File "/Users/jelle/py/black/src/black/__init__.py", line 2731, in transform_line
    result.extend(
  File "/Users/jelle/py/black/src/black/__init__.py", line 2725, in transform_line
    for transformed_line in transform(line, features):
  File "/Users/jelle/py/black/src/black/__init__.py", line 2834, in __call__
    for line_result in self.do_transform(line, string_idx):
  File "/Users/jelle/py/black/src/black/__init__.py", line 3315, in do_transform
    append_leaves(new_line, line, LL[: string_idx - 1])
  File "/Users/jelle/py/black/src/black/__init__.py", line 4601, in append_leaves
    new_line.append(new_leaf)
  File "/Users/jelle/py/black/src/black/__init__.py", line 1425, in append
    self.bracket_tracker.mark(leaf)
  File "/Users/jelle/py/black/src/black/__init__.py", line 1291, in mark
    opening_bracket = self.bracket_match.pop((self.depth, leaf.type))
KeyError: (-1, 10)
error: cannot format author.py: (-1, 10)
Oh no! 💥 💔 💥
1 file failed to reformat.