Fix two problem when we create multiple instances of the same dataset (2 for-loops)

-- Iterator list is keeping  all created iterators wihtout cleaning them up
-- alter tree modifies the original.

mindspore/ccsrc/dataset/api/python_bindings.cc

@@ -225,11 +225,13 @@ void bindTensor(py::module *m) {
   (void)py::class_<DataType>(*m, "DataType")
     .def(py::init<std::string>())
     .def(py::self == py::self)
-    .def("__str__", &DataType::ToString);
+    .def("__str__", &DataType::ToString)
+    .def("__deepcopy__", [](py::object &t, py::dict memo) { return t; });
 }
 
 void bindTensorOps1(py::module *m) {
-  (void)py::class_<TensorOp, std::shared_ptr<TensorOp>>(*m, "TensorOp");
+  (void)py::class_<TensorOp, std::shared_ptr<TensorOp>>(*m, "TensorOp")
+    .def("__deepcopy__", [](py::object &t, py::dict memo) { return t; });
 
   (void)py::class_<NormalizeOp, TensorOp, std::shared_ptr<NormalizeOp>>(
     *m, "NormalizeOp", "Tensor operation to normalize an image. Takes mean and std.")

mindspore/dataset/engine/iterators.py

@@ -15,6 +15,8 @@
 """Built-in iterators.
 """
 from abc import abstractmethod
+import copy
+import weakref
 
 from mindspore._c_dataengine import DEPipeline
 from mindspore._c_dataengine import OpName
@@ -27,7 +29,9 @@ ITERATORS_LIST = list()
 
 def _cleanup():
     for itr in ITERATORS_LIST:
-        itr.release()
+        iter_ref = itr()
+        if itr is not None:
+            iter_ref.release()
 
 
 def alter_tree(node):
@@ -73,8 +77,10 @@ class Iterator:
     """
 
     def __init__(self, dataset):
-        ITERATORS_LIST.append(self)
-        self.dataset = alter_tree(dataset)
+        ITERATORS_LIST.append(weakref.ref(self))
+        # create a copy of tree and work on it.
+        self.dataset = copy.deepcopy(dataset)
+        self.dataset = alter_tree(self.dataset)
         if not self.__is_tree():
             raise ValueError("The data pipeline is not a tree (i.e., one node has 2 consumers)")
         self.depipeline = DEPipeline()