格式化字符串中的python dict [复制](python dict in formatted string [duplicate])

 将Base类引用分配给Derived类引用变量是非法的。 
 
 X类型的变量只能是对X类型或派生类型的对象的引用。 
 
 您可能需要另一个包含与现有对象相同数据的SpecialContact实例。 没有办法避免手动复制。 
 
 当我需要将匹配属性从一个对象复制到另一个不兼容的对象时，我使用以下扩展方法（1）： 
 
public static void AssignFrom(this object destination, object source) {
  Type dest_type = destination.GetType();
  Type source_type = source.GetType();

  var matching_props = from d in dest_type.GetProperties()
                        join s in source_type.GetProperties()
                        on d.Name equals s.Name
                        where d.IsWritable() && s.IsReadable()
                        select new {
                          source = s,
                          destination = d
                        };

  foreach (var prop in matching_props) {
    prop.destination.SetValue(destination, prop.source.GetValue(source, null), null);
  }
}
 
 那你可以这样做： 
 
specialContact.assignFrom(contact);
 
 请考虑这个解决方法。 正确的解决方案是正确设计您的类层次结构，而您不会遇到此问题。 
 
 
 1注意：它按名称匹配属性并假定它们属于同一类型。 

It is illegal to assign Base class reference to the Derived class reference variable.
 
Variable of type X can only be a reference to an object of type X or derived.
 
You probably need to have another instance of SpecialContact which contains the same data as existing object. There is no way to avoid manual copying. 
 
I use the following extension method when I need to copy the matching properties from one object to another incompatible one(1): 
 
public static void AssignFrom(this object destination, object source) {
  Type dest_type = destination.GetType();
  Type source_type = source.GetType();

  var matching_props = from d in dest_type.GetProperties()
                        join s in source_type.GetProperties()
                        on d.Name equals s.Name
                        where d.IsWritable() && s.IsReadable()
                        select new {
                          source = s,
                          destination = d
                        };

  foreach (var prop in matching_props) {
    prop.destination.SetValue(destination, prop.source.GetValue(source, null), null);
  }
}
 
Then you can do: 
 
specialContact.assignFrom(contact);
 
Please consider this a workaround. The proper solution would be to design properly your class hierarchy where you do not come to this problem.
 
 
1 Note: it matches the properties by name and assumes they are of the same type.