bugfix for hang in list(Batch()) (#117)

tianshou/data/batch.py

@@ -433,6 +433,14 @@ class Batch:
         """Return self[k] if k in self else d. d defaults to None."""
         return self.__dict__.get(k, d)
 
+    def __iter__(self):
+        try:
+            length = len(self)
+        except Exception:
+            length = 0
+        for i in range(length):
+            yield self[i]
+
     def to_numpy(self) -> None:
         """Change all torch.Tensor to numpy.ndarray. This is an in-place
         operation.