initial commit of AbtractAttrDef the abstract attribute definition

openpype/pipeline/lib/attribute_definitions.py

@@ -0,0 +1,24 @@
+from abc import ABCMeta, abstractmethod
+import six
+
+
+@six.add_metaclass(ABCMeta)
+class AbtractAttrDef:
+    """Abstraction of attribute definiton.
+
+    Each attribute definition must have implemented validation and
+    conversion method.
+
+    Attribute definition should have ability to return "default" value. That
+    can be based on passed data into `__init__` so is not abstracted to
+    attribute.
+    """
+
+    @abstractmethod
+    def convert_value(self, value):
+        """Convert value to a valid one.
+
+        Convert passed value to a valid type. Use default if value can't be
+        converted.
+        """
+        pass