fix append batch over batch

docs/tutorials/concepts.rst

@@ -8,6 +8,12 @@ Tianshou splits a Reinforcement Learning agent training procedure into these par
     :height: 300
 
 
+Here is a more detailed description, where ``Env`` is the environment and ``Model`` is the neural network:
+
+.. image:: /_static/images/concepts_arch2.png
+    :align: center
+    :height: 300
+
 Data Batch
 ----------
 

test/base/test_batch.py

@@ -34,6 +34,16 @@ def test_batch_over_batch():
     print(batch2)
     assert batch2.values()[-1] == batch2.c
     assert batch2[-1].b.b == 0
+    batch2.append(Batch(c=[6, 7, 8], b=batch))
+    assert batch2.c == [6, 7, 8, 6, 7, 8]
+    assert batch2.b.a == [3, 4, 5, 3, 4, 5]
+    assert batch2.b.b == [4, 5, 0, 4, 5, 0]
+    d = {'a': [3, 4, 5], 'b': [4, 5, 6]}
+    batch3 = Batch(c=[6, 7, 8], b=d)
+    batch3.append(Batch(c=[6, 7, 8], b=d))
+    assert batch3.c == [6, 7, 8, 6, 7, 8]
+    assert batch3.b.a == [3, 4, 5, 3, 4, 5]
+    assert batch3.b.b == [4, 5, 6, 4, 5, 6]
 
 
 def test_batch_over_batch_to_torch():

tianshou/data/batch.py

@@ -234,6 +234,8 @@ class Batch:
                 self.__dict__[k] = torch.cat([self.__dict__[k], v])
             elif isinstance(v, list):
                 self.__dict__[k] += v
+            elif isinstance(v, Batch):
+                self.__dict__[k].append(v)
             else:
                 s = f'No support for append with type \
                       {type(v)} in class Batch.'