fix dataloader (#28105)

python/paddle/fluid/dataloader/dataloader_iter.py

@@ -17,6 +17,7 @@ import six
 import sys
 import time
 import signal
+import numbers
 import logging
 import itertools
 import threading
@@ -81,12 +82,17 @@ def default_collate_fn(batch):
             else:
                 slots[i].append(item)
 
-    if isinstance(slots[0][0], np.ndarray):
-        return [np.stack(slot, axis=0) for slot in slots]
-    elif isinstance(slots[0][0], paddle.Tensor):
-        return [layers.stack(slot, axis=0) for slot in slots]
+    outputs = []
+    for slot in slots:
+        if isinstance(slot[0], (np.ndarray, np.bool, numbers.Number)):
+            tmp = np.stack(slot, axis=0)
+            outputs.append(tmp)
+        elif isinstance(slot[0], paddle.Tensor):
+            tmp = layers.stack(slot, axis=0)
+            outputs.append(tmp)
         else:
-        raise RuntimeError("Unknown data type {}".format(type(slots[0][0])))
+            raise RuntimeError("Unknown data type {}".format(type(slot[0])))
+    return outputs
 
 
 class _DatasetKind(object):