first pass that transition collection interface

rl_coach/memories/non_episodic/transition_collection.py

@@ -0,0 +1,35 @@
+from rl_coach.core_types import Transition
+
+
+class TransitionCollection(object):
+    """
+    Simple python implementation of transitions collection non-episodic memories
+    are constructed on top of.
+    """
+    def __init__(self):
+        super(TransitionCollection, self).__init__()
+
+    def append(self, transition):
+        pass
+
+    def extend(self, transitions):
+        for transition in transitions:
+            self.append(transition)
+
+    def __len__(self):
+        pass
+
+    def __del__(self, range: slice):
+        # NOTE: the only slice used is the form: slice(None, n)
+        # NOTE: if it is easier, what we really want here is the ability to
+        # constrain the size of the collection.
+        pass
+
+    def __getitem__(self, key: int):
+        # NOTE: we can switch to a method which fetches multiple items at a time
+        # if that would significantly improve performance
+        pass
+
+    def __iter__(self):
+        # this is not high priority
+        pass