Added Element dataclass

core/element.py

@@ -0,0 +1,31 @@
+from dataclasses import dataclass, asdict, astuple
+from typing import TypeVar, Generic, Optional
+
+# Some typing information for Python static type checkers
+Literal = TypeVar('Literal', int, float, bool, str)  # Must be int, float, bool or str
+
+
+@dataclass
+class Element(Generic[Literal]):
+    """
+    An Element can represent one of following two things, based on the value of its attributes:
+
+    *   An element (node or edge) in the State (id is not None). In this case the value can be None because it hasn't
+        yet been read OR because the element doesn't have a value.
+    *   A value for which a node has not yet been materialized in the State (id is None, value is not None).
+
+
+    If you are familiar with the Modelverse Kernel, this class serves a function similar to the {id: ..., value: ...}
+    dict that is used there.
+    """
+    id: Optional[str] = None
+    value: Optional[Literal] = None
+
+    def is_none(self) -> bool:
+        return self.id is None and self.value is None
+
+
+String = Element[str]
+Integer = Element[int]
+Float = Element[float]
+Boolean = Element[bool]