 }
 
 /// An error produced by a failable Python operation.
-@frozen
 public enum PythonError : Error, Equatable {
   /// A Python runtime exception, produced by calling a Python function.
   case exception(PythonObject, traceback: PythonObject?)

/// a Python C API `PyObject`.
@dynamicCallable
@dynamicMemberLookup
@frozen
public struct PythonObject {
  /// The underlying `PyReference`.
  fileprivate var reference: PyReference

/// Member access operations return an `Optional` result. When member access
/// fails, `nil` is returned.
@dynamicMemberLookup
public struct CheckingPythonObject {
  /// The underlying `PythonObject`.
  private var base: PythonObject
