diff --git a/paddle/framework/tensor.h b/paddle/framework/tensor.h
index 4b5a2ae523f2f7fde5445f0534cd99969ad9d59e..f040c09c089ec75c9773d752685be5e232e8f4b7 100644
--- a/paddle/framework/tensor.h
+++ b/paddle/framework/tensor.h
@@ -29,16 +29,19 @@ limitations under the License. */
 
 namespace paddle {
 
-namespace framework {
+namespace pybind {
 namespace details {
 template <bool less, size_t i, typename... args>
 struct CastToPyBufferImpl;
 }
+}  // namespace pybind
+
+namespace framework {
 
 class Tensor {
  public:
   template <bool less, size_t i, typename... args>
-  friend struct details::CastToPyBufferImpl;
+  friend struct pybind::details::CastToPyBufferImpl;
 
   template <typename T, size_t D, int MajorType, typename IndexType>
   friend struct EigenTensor;
@@ -165,12 +168,6 @@ class Tensor {
   /*! points to dimensions of memory block. */
   DDim dims_;
 
-  /**
-   * A cache of the number of elements in a tensor.
-   * Would be 0 for an uninitialized tensor.
-   */
-  int64_t numel_;
-
   /**
    * @brief   A PlaceHolder may be shared by more than one tensor.
    *
diff --git a/paddle/framework/tensor_impl.h b/paddle/framework/tensor_impl.h
index 6d2c14f4c47afb755b1c74f6dc4dd10ab25ed191..a5405f9c31543b5733f9db923c2a6f8b968cfc2d 100644
--- a/paddle/framework/tensor_impl.h
+++ b/paddle/framework/tensor_impl.h
@@ -147,13 +147,12 @@ inline Tensor Tensor::Slice(const int& begin_idx, const int& end_idx) const {
 
 inline Tensor& Tensor::Resize(const DDim& dims) {
   dims_ = dims;
-  numel_ = product(dims_);
   return *this;
 }
 
 inline const DDim& Tensor::dims() const { return dims_; }
 
-inline int64_t Tensor::numel() const { return numel_; }
+inline int64_t Tensor::numel() const { return product(dims_); }
 
 template <typename T>
 inline Tensor ReshapeToMatrix(const Tensor& src, int num_col_dims) {
diff --git a/paddle/operators/elementwise_add_op.h b/paddle/operators/elementwise_add_op.h
index 42a7a29e991adcce98c74c62bb359a2cc4a7c30d..9e9f1ffba6fb23f5394713c67aa4363b85717f50 100644
--- a/paddle/operators/elementwise_add_op.h
+++ b/paddle/operators/elementwise_add_op.h
@@ -12,6 +12,8 @@
    See the License for the specific language governing permissions and
    limitations under the License. */
 
+#pragma once
+
 #include "paddle/operators/elementwise_op.h"
 
 namespace paddle {
diff --git a/paddle/operators/elementwise_div_op.h b/paddle/operators/elementwise_div_op.h
index 6ef60cdf8dfc01f7cf51bb68f18900effb444fca..9bd7c8ea548c46ec9b4c5a085e4e70d5dd162f3a 100644
--- a/paddle/operators/elementwise_div_op.h
+++ b/paddle/operators/elementwise_div_op.h
@@ -12,6 +12,8 @@
    See the License for the specific language governing permissions and
    limitations under the License. */
 
+#pragma once
+
 #include "paddle/operators/elementwise_op.h"
 
 namespace paddle {
diff --git a/paddle/operators/elementwise_sub_op.h b/paddle/operators/elementwise_sub_op.h
index faa38cf4014e98b2a28f51b32585ca5c10289841..f6bc66cd0e1594a8bc7070e2f182401b92d1c88e 100644
--- a/paddle/operators/elementwise_sub_op.h
+++ b/paddle/operators/elementwise_sub_op.h
@@ -12,6 +12,7 @@
    See the License for the specific language governing permissions and
    limitations under the License. */
 
+#pragma once
 #include "paddle/operators/elementwise_op.h"
 
 namespace paddle {
diff --git a/paddle/pybind/pybind.cc b/paddle/pybind/pybind.cc
index c7009a604f60cda11434ad33b6c7d7caee1befdd..fbe074188e5870de4b00fa4fff733035739974ea 100644
--- a/paddle/pybind/pybind.cc
+++ b/paddle/pybind/pybind.cc
@@ -34,12 +34,7 @@ limitations under the License. */
 namespace py = pybind11;
 
 namespace paddle {
-namespace framework {
-
-using Tensor = framework::Tensor;
-using LoDTensor = framework::LoDTensor;
-using LoD = framework::LoD;
-
+namespace pybind {
 static size_t UniqueIntegerGenerator() {
   static std::atomic<size_t> generator;
   return generator.fetch_add(1);
@@ -56,6 +51,10 @@ bool IsCompileGPU() {
 PYBIND11_PLUGIN(core) {
   py::module m("core", "C++ core of PaddlePaddle");
 
+  // using framework in this function. Since it is inside a function, it will
+  // not cause namespace pollution.
+  using namespace paddle::framework;  // NOLINT
+
   py::class_<Tensor>(m, "Tensor", py::buffer_protocol())
       .def_buffer(
           [](Tensor &self) -> py::buffer_info { return CastToPyBuffer(self); })
@@ -107,7 +106,7 @@ PYBIND11_PLUGIN(core) {
 #ifdef PADDLE_ONLY_CPU
             new (&instance) LoDTensor(lod);
 #else
-             paddle::framework::LoD new_lod;
+             LoD new_lod;
              new_lod.reserve(lod.size());
              std::copy(lod.begin(), lod.end(), std::back_inserter(new_lod));
              new (&instance) LoDTensor(new_lod);
@@ -118,7 +117,7 @@ PYBIND11_PLUGIN(core) {
 #ifdef PADDLE_ONLY_CPU
              self.set_lod(lod);
 #else
-             paddle::framework::LoD new_lod;
+             LoD new_lod;
              new_lod.reserve(lod.size());
              std::copy(lod.begin(), lod.end(), std::back_inserter(new_lod));
              self.set_lod(new_lod);
@@ -132,7 +131,7 @@ PYBIND11_PLUGIN(core) {
            std::vector<std::vector<size_t>> new_lod;
            new_lod.reserve(lod.size());
            std::transform(lod.begin(), lod.end(), std::back_inserter(new_lod),
-               [](paddle::framework::Vector<size_t> item) ->
+               [](Vector<size_t> item) ->
                    std::vector<size_t> {
                  std::vector<size_t> v;
                  v.reserve(item.size());
@@ -317,5 +316,5 @@ All parameter, weight, gradient are variables in Paddle.
 
   return m.ptr();
 }
-}  // namespace framework
+}  // namespace pybind
 }  // namespace paddle
diff --git a/paddle/pybind/tensor_py.h b/paddle/pybind/tensor_py.h
index 95171acf729a513e5c92d1e0cba15cb12b38561a..bcfba84a1aa6e646cf255dc4612dfda42169fc44 100644
--- a/paddle/pybind/tensor_py.h
+++ b/paddle/pybind/tensor_py.h
@@ -23,7 +23,7 @@ namespace py = pybind11;
 
 namespace paddle {
 
-namespace framework {
+namespace pybind {
 
 namespace details {