Enable proper shallow copying of state mutable sequences

This gives similar behaviour to a standard list

stonesoup/sensormanager/reward.py

@@ -95,8 +95,6 @@ def __call__(self, config: Mapping[Sensor, Sequence[Action]], tracks: Set[Track]
         predicted_tracks = set()
         for track in tracks:
             predicted_track = copy.copy(track)
-            predicted_track.states = copy.copy(predicted_track.states)
-            predicted_track.metadatas = copy.copy(predicted_track.metadatas)
             predicted_track.append(self.predictor.predict(predicted_track, timestamp=metric_time))
             predicted_tracks.add(predicted_track)
 

stonesoup/types/state.py

@@ -1,3 +1,4 @@
+import copy
 import datetime
 import uuid
 from collections import abc
@@ -172,6 +173,11 @@ class StateMutableSequence(Type, abc.MutableSequence):
     proxying state attributes to the last state in the sequence. This sequence
     can also be indexed/sliced by :class:`datetime.datetime` instances.
 
+    Notes
+    -----
+    If shallow copying, similar to a list, it is safe to add/remove states
+    without effecting the original sequence.
+
     Example
     -------
     >>> t0 = datetime.datetime(2018, 1, 1, 14, 00)
@@ -261,6 +267,13 @@ def __getattribute__(self, name):
                     # raise the original error instead
                     raise original_error
 
+    def __copy__(self):
+        inst = self.__class__.__new__(self.__class__)
+        inst.__dict__.update(self.__dict__)
+        property_name = self.__class__.states._property_name
+        inst.__dict__[property_name] = copy.copy(self.__dict__[property_name])
+        return inst
+
     def insert(self, index, value):
         return self.states.insert(index, value)
 

stonesoup/types/tests/test_state.py

@@ -1,3 +1,4 @@
+import copy
 import datetime
 
 import numpy as np
@@ -516,6 +517,23 @@ def complicated_attribute(self):
         _ = test_obj.complicated_attribute
 
 
+def test_state_mutable_sequence_copy():
+    state_vector = StateVector([[0]])
+    timestamp = datetime.datetime(2018, 1, 1, 14)
+    delta = datetime.timedelta(minutes=1)
+    sequence = StateMutableSequence(
+        [State(state_vector, timestamp=timestamp+delta*n)
+         for n in range(10)])
+
+    sequence2 = copy.copy(sequence)
+
+    assert sequence2.states is not sequence.states
+
+    assert sequence2[-1] is sequence[-1]
+    sequence2.remove(sequence[-1])
+    assert sequence2[-1] is not sequence[-1]
+
+
 def test_from_state():
     start = datetime.datetime.now()
     kwargs = {"state_vector": np.arange(4), "timestamp": start}

stonesoup/types/track.py

@@ -1,3 +1,4 @@
+import copy
 import uuid
 from typing import MutableSequence, MutableMapping
 
@@ -47,6 +48,11 @@ def __setitem__(self, index, value):
             index = len(self.states) + index
         self._update_metadatas(index)
 
+    def __copy__(self):
+        inst = super().__copy__()
+        inst.__dict__['metadatas'] = copy.copy(self.__dict__['metadatas'])
+        return inst
+
     def insert(self, index, value):
         """Insert value at index of :attr:`states`.