В чем разница между старым и новым стилем классов в Python?

Вы можете посмотреть PostSharp . Они даже имеют образец в Связывании данных . Код, взятый оттуда:

/// 

/// Aspect that, when apply on a class, fully implements the interface 
///  into that class, and overrides all properties to
/// that they raise the event .
/// 
[Serializable]
[IntroduceInterface( typeof(INotifyPropertyChanged), 
                     OverrideAction = InterfaceOverrideAction.Ignore )]
[MulticastAttributeUsage( MulticastTargets.Class, 
                          Inheritance = MulticastInheritance.Strict )]
public sealed class NotifyPropertyChangedAttribute : InstanceLevelAspect, 
                                                     INotifyPropertyChanged
{

    /// 

    /// Field bound at runtime to a delegate of the method OnPropertyChanged.
    /// 
    [ImportMember( "OnPropertyChanged", IsRequired = false)] 
    public Action OnPropertyChangedMethod;

    /// 

    /// Method introduced in the target type (unless it is already present);
    /// raises the  event.
    /// 
    /// Name of the property.
    [IntroduceMember( Visibility = Visibility.Family, IsVirtual = true, 
                      OverrideAction = MemberOverrideAction.Ignore )]
    public void OnPropertyChanged( string propertyName )
    {
        if ( this.PropertyChanged != null )
        {
           this.PropertyChanged( this.Instance, 
                                  new PropertyChangedEventArgs( propertyName ) );
        }
    }

    /// 

    /// Event introduced in the target type (unless it is already present);
    /// raised whenever a property has changed.
    /// 
    [IntroduceMember( OverrideAction = MemberOverrideAction.Ignore )]
    public event PropertyChangedEventHandler PropertyChanged;

    /// 

    /// Method intercepting any call to a property setter.
    /// 
    /// Aspect arguments.
    [OnLocationSetValueAdvice, 
     MulticastPointcut( Targets = MulticastTargets.Property, 
         Attributes = MulticastAttributes.Instance)]
    public void OnPropertySet( LocationInterceptionArgs args )
    {
        // Don't go further if the new value is equal to the old one.
        // (Possibly use object.Equals here).
        if ( args.Value == args.GetCurrentValue() ) return;

        // Actually sets the value.
        args.ProceedSetValue();

        // Invoke method OnPropertyChanged (our, the base one, or the overridden one).
        this.OnPropertyChangedMethod.Invoke( args.Location.Name );

    }
}

Использование так же просто:

[NotifyPropertyChanged]
public class Shape
{
   public double X { get; set; }
   public double Y { get; set; }
}

Примеры, взятые с сайта PostSharp и вставленные для завершения ответа