@Nullable
  default PyAstExpression getCallee() {
    // peel off any parens, because we may have smth like (lambda x: x+1)(2)
    PsiElement seeker = getFirstChild();
    while (seeker instanceof PyAstParenthesizedExpression) seeker = ((PyAstParenthesizedExpression)seeker).getContainedExpression();
    return seeker instanceof PyAstExpression ? (PyAstExpression) seeker : null;
  }
@Nullable
  default PyAstExpression getCallee()