Changin Sampler in Python to SamplerObj

mindspore/ccsrc/minddata/dataset/engine/consumers/tree_consumer.cc

@@ -593,6 +593,8 @@ Status DatasetSizeGetter::GetRow(const std::shared_ptr<TreeAdapter> &tree_adapte
 }
 Status DatasetSizeGetter::Terminate() {
   for (const auto &tree : tree_adapters_) {
+    RETURN_UNEXPECTED_IF_NULL(tree);
+    RETURN_UNEXPECTED_IF_NULL(tree->AllTasks());
     RETURN_IF_NOT_OK(tree->AllTasks()->ServiceStop());
   }
   return Status::OK();

mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/source/minddata_node.cc

@@ -187,7 +187,7 @@ Status MindDataNode::GetDatasetSize(const std::shared_ptr<DatasetSizeGetter> &si
     *dataset_size = dataset_size_;
     return Status::OK();
   }
-  int64_t num_rows;
+  int64_t num_rows = -1;
   std::vector<std::shared_ptr<ShardOperator>> operators;
   RETURN_IF_NOT_OK(BuildMindDatasetSamplerChain(sampler_, &operators, num_padded_));