actually the whole code has been refactored

orchestrator/model/resources.py

+import copy
+import json
 import uuid
 
 from enum import Enum
-from voluptuous import Schema, Invalid, MultipleInvalid
+from voluptuous import Schema, Invalid, MultipleInvalid, Any, ALLOW_EXTRA, PREVENT_EXTRA
 
 
 class Resource(object):
     DEFAULT_ID_LENGTH = 8
+    ADDITIONAL_SCHEMA = {}
+
+    def __new__(cls, *args, **kwargs):
+        attributes = cls.__attributes_from_dict(args[0] if len(args) else kwargs)
+        resource_type = attributes['type'].value
+        if resource_type is Resource:
+            raise InvalidResourceException('Resource class is abstract')
+        cls.__validate_attributes(attributes, cls.__schema(resource_type, extend=True))
+        instance = super(Resource, resource_type).__new__(resource_type)
+        instance._attributes = attributes  # pylint: disable=protected-access
+        return instance
 
-    def __init__(self, *args, **kwargs):
-        if len(args):
-            resource = args[0]
-            if isinstance(resource, Resource):
-                self.__id = resource.id
-                self.__type = Resource.Type[resource.type]
-            else:
-                self.__attributes_from_dict(resource)
-        else:
-            self.__attributes_from_dict(kwargs)
-
-    def __attributes_from_dict(self, attributes):
-        schema = Schema({
-            'id': str,
-            'type': Resource.Type.validate
-        })
+    @classmethod
+    def __attributes_from_dict(cls, attributes):
+        cls.__validate_attributes(attributes, cls.__schema(extend=False))
+        attributes = copy.deepcopy(attributes)
+        attributes['id'] = attributes.get('id', Resource.__generate_random_id())
+        attributes['type'] = ResourceType.validate(attributes.get('type', cls))
+        return attributes
+
+    @classmethod
+    def __validate_attributes(cls, attributes, schema):
         try:
             schema(attributes)
-            self.__id = attributes.get('id', Resource._random_id())
-            self.__type = Resource.Type[attributes.get('type', 'null')]
         except MultipleInvalid as invalid:
             raise InvalidResourceException(invalid)
 
-    @property
-    def id(self):
-        return self.__id
+    @classmethod
+    def __schema(cls, resource_type=None, extend=False):
+        try:
+            string_validator = Any(str, unicode)
+        except NameError:
+            string_validator = Any(str)
+
+        schema = Schema(schema={'id': string_validator, 'type': ResourceType.validate}, extra=ALLOW_EXTRA)
+        if extend:
+            additional = resource_type.ADDITIONAL_SCHEMA if resource_type else cls.ADDITIONAL_SCHEMA
+            schema = schema.extend(additional, extra=PREVENT_EXTRA)
+        return schema
 
     @property
     def type(self):
-        return self.__type.name
+        return str(self._attributes['type'])
+
+    def __getattr__(self, item):
+        try:
+            return self._attributes[item]
+        except KeyError:
+            raise AttributeError('Attribute (%s) is not set on resource')
 
     @staticmethod
-    def _random_id():
+    def __generate_random_id():
         return uuid.uuid4().hex[:Resource.DEFAULT_ID_LENGTH]
 
     def __eq__(self, other):
-        return isinstance(other, Resource) and \
-               self.id == other.id and \
-               self.type == other.type
+        try:
+            for attr, other_value in other.items():
+                value = self._attributes.get(attr)
+                if value is None or value != other_value:
+                    return False
+            return True
+        except AttributeError:
+            return False
 
     def __repr__(self):
-        return "%s(%s)" % (self.__class__.__name__, self.id)
+        return json.dumps(self, default=Resource.json_encoder)
 
-    def __hash__(self):
-        return hash(self.__repr__())
+    def __iter__(self):
+        return self._attributes.__iter__()
 
-    class Type(Enum):
-        null = 0
-        instance = 1
+    def keys(self):
+        return self._attributes.keys()
 
-        @classmethod
-        def validate(cls, value):
-            try:
-                cls[value]
-            except KeyError:
-                raise Invalid('The given resource type (%s) is not valid' % value)
-            return True
+    def values(self):
+        return self._attributes.values()
 
+    def items(self):
+        return self._attributes.items()
 
-class Instance(Resource):
-    def __init__(self, *args, **kwargs):
-        kwargs['type'] = Resource.Type.instance.name
-        super(Instance, self).__init__(*args, **kwargs)
+    def __getitem__(self, item):
+        return self._attributes[item]
 
+    def __add__(self, other):
+        return ResourceGroup(resources=[self, other])
+
+    @staticmethod
+    def json_encoder(data):
+        if isinstance(data, ResourceType):
+            return str(data)
+        return dict(data)
+
+
+class ResourceGroup(Resource):
+    ADDITIONAL_SCHEMA = {
+        'resources': Any(list, set, tuple)
+    }
+
+    def __init__(self, *_, **__):
+        self.__resources = {}
+        if 'resources' in self._attributes.keys():
+            for resource in self._attributes['resources']:
+                self.add(resource)
+        self._attributes['resources'] = self.resources
+
+    def add(self, resource):
+        if not isinstance(resource, Resource):
+            try:
+                resource = Resource(resource)
+            except InvalidResourceException:
+                raise InvalidResourceException('ResourceGroup can only store resources')
+        self.__resources[resource.id] = resource
 
-class ResourceGroup(object):
-    def __init__(self, *args):
-        self.__resources = set()
-        if len(args):
-            for argument in args:
+    def remove(self, resource):
         try:
-                    self.__iadd__(argument)
+            del self.__resources[Resource(resource).id]
         except InvalidResourceException:
-                    for resource in argument:
-                        self.__iadd__(resource)
+            del self.__resources[resource.id]
 
     @property
     def resources(self):
-        return list(self.__resources)
+        return list(self.__resources.values())
 
-    def __add__(self, other):
-        if isinstance(other, dict):
-            return ResourceGroup(Resource(other), *self.resources)
-        if isinstance(other, Resource):
-            return ResourceGroup(other, *self.resources)
-        if isinstance(other, ResourceGroup):
-            resources = other.resources + self.resources
-            return ResourceGroup(*resources)
-        raise InvalidResourceException()
-
-    def __iadd__(self, other):
-        if isinstance(other, dict):
-            self.__resources.add(Resource(other))
-            return self
-        if isinstance(other, Resource):
-            self.__resources.add(other)
-            return self
-        if isinstance(other, ResourceGroup):
-            self.__resources.union(other.resources)
-            return self
-        raise InvalidResourceException()
 
-    def __iter__(self):
-        return self.__resources.__iter__()
+class Instance(Resource):
+    ADDITIONAL_SCHEMA = {
+        'number_of_cores': int
+    }
 
-    def __eq__(self, other):
-        return self.__resources == set(other.resources)
+
+class ResourceType(Enum):
+    null = Resource
+    group = ResourceGroup
+    instance = Instance
+
+    @classmethod
+    def validate(cls, value):
+        if isinstance(value, cls):
+            return value
+        try:
+            return cls[value]
+        except KeyError:
+            return cls(value)
+        except ValueError:
+            raise Invalid('The given resource type (%s) is not valid' % value)
+
+    def __str__(self):
+        return str(self.name)
+
+    def __repr__(self):
+        return '%s(%s)' % (self.__class__.__name__, str(self))
 
 
 class InvalidResourceException(Exception):