Added order by functions

src/cpl_query/extension/ordered_iterable_abc.py

@@ -0,0 +1,20 @@
+from abc import abstractmethod
+from collections import Callable
+
+from cpl_query.extension.iterable_abc import IterableABC
+
+
+class OrderedIterableABC(IterableABC):
+
+    @abstractmethod
+    def __init__(self, _func: Callable = None):
+        IterableABC.__init__(self)
+        self._funcs: list[Callable] = []
+        if _func is not None:
+            self._funcs.append(_func)
+
+    @abstractmethod
+    def then_by(self, func: Callable) -> 'OrderedIterableABC': pass
+
+    @abstractmethod
+    def then_by_descending(self, func: Callable) -> 'OrderedIterableABC': pass