Fix Python API.

python/paddle/v2/framework/layers.py

@@ -372,11 +372,13 @@ def sequence_pool(input, pool_type, **kwargs):
     helper = LayerHelper('sequence_pool', input=input, **kwargs)
     dtype = helper.input_dtype()
     pool_out = helper.create_tmp_variable(dtype)
+    max_index = helper.create_tmp_variable(dtype)
 
     helper.append_op(
         type="sequence_pool",
-        inputs={"X": [input]},
-        outputs={"Out": [pool_out]},
+        inputs={"X": input},
+        outputs={"Out": pool_out,
+                 "MaxIndex": max_index},
         attrs={"pooltype": pool_type.upper()})
 
     return pool_out