@Nullable
  default PyAstExpression getAssignedValue() {
    PsiElement child = getLastChild();
    while (child != null && !(child instanceof PyAstExpression)) {
      if (child instanceof PsiErrorElement) return null; // incomplete assignment operator can't be analyzed properly, bail out.
      child = child.getPrevSibling();
    }
    return (PyAstExpression)child;
  }
@Nullable
  default PyAstExpression getAssignedValue()