Example:

# x.py
class C:
  @property
  def p(self) -> int:
    return 0

$ ./python -E x.py
python: ../Python/ast.c:724: ast_for_arguments: Assertion `((n)->n_type) == 263 || ((n)->n_type) == 267' failed.
Aborted
$

Removing "@property" or "-> int" from the example avoids the problem.  Adding argument annotations inside the argument list doesn't trigger it.