[MXNET-545] Fix broken cython build

CMakeLists.txt

@@ -50,6 +50,7 @@ mxnet_option(USE_SIGNAL_HANDLER   "Print stack traces on segfaults." OFF)
 mxnet_option(USE_TENSORRT         "Enable infeference optimization with TensorRT." OFF)
 mxnet_option(USE_ASAN             "Enable Clang/GCC ASAN sanitizers." OFF)
 mxnet_option(ENABLE_TESTCOVERAGE  "Enable compilation with test coverage metric output" OFF)
+mxnet_option(BUILD_CYTHON_MODULES "Build cython modules." OFF)
 
 message(STATUS "CMAKE_CROSSCOMPILING ${CMAKE_CROSSCOMPILING}")
 message(STATUS "CMAKE_HOST_SYSTEM_PROCESSOR ${CMAKE_HOST_SYSTEM_PROCESSOR}")
@@ -806,3 +807,12 @@ endif()
 set(LINT_DIRS "include src plugin cpp-package tests")
 set(EXCLUDE_PATH "src/operator/contrib/ctc_include")
 add_custom_target(mxnet_lint COMMAND ${CMAKE_COMMAND} -DMSVC=${MSVC} -DPYTHON_EXECUTABLE=${PYTHON_EXECUTABLE} -DLINT_DIRS=${LINT_DIRS} -DPROJECT_SOURCE_DIR=${CMAKE_CURRENT_SOURCE_DIR} -DPROJECT_NAME=mxnet -DEXCLUDE_PATH=${EXCLUDE_PATH} -P ${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/dmlc-core/cmake/lint.cmake)
+
+if(BUILD_CYTHON_MODULES)
+  include(cmake/BuildCythonModules.cmake)
+  add_cython_modules(2) # Build cython module for python2 if python2 is found
+  add_cython_modules(3) # Build cython module for python3 if python3 is found
+  if((NOT ${PYTHON2_FOUND}) AND (NOT ${PYTHON3_FOUND}))
+    message(FATAL_ERROR "No python interpreter found to build cython modules")
+  endif()
+endif()

Makefile

@@ -630,7 +630,7 @@ doxygen:
 
 # Cython build
 cython:
-	cd python; python setup.py build_ext --inplace --with-cython
+	cd python; $(PYTHON) setup.py build_ext --inplace --with-cython
 
 cython2:
 	cd python; python2 setup.py build_ext --inplace --with-cython

ci/Jenkinsfile_utils.groovy

@@ -67,7 +67,7 @@ def pack_lib(name, libs, include_gcov_data = false) {
   sh returnStatus: true, script: """
 set +e
 echo "Packing ${libs} into ${name}"
-echo ${libs} | sed -e 's/,/ /g' | xargs md5sum
+for i in \$(echo ${libs} | sed -e 's/,/ /g'); do md5sum \$i; done
 return 0
 """
   stash includes: libs, name: name
@@ -86,7 +86,7 @@ def unpack_and_init(name, libs, include_gcov_data = false) {
   sh returnStatus: true, script: """
 set +e
 echo "Unpacked ${libs} from ${name}"
-echo ${libs} | sed -e 's/,/ /g' | xargs md5sum
+for i in \$(echo ${libs} | sed -e 's/,/ /g'); do md5sum \$i; done
 return 0
 """
   if (include_gcov_data) {

ci/docker/install/ubuntu_python.sh

@@ -30,5 +30,5 @@ wget -nv https://bootstrap.pypa.io/get-pip.py
 python3 get-pip.py
 python2 get-pip.py
 
-pip2 install nose cpplint==1.3.0 pylint==1.9.3 'numpy<=1.15.2,>=1.8.2' nose-timer 'requests<2.19.0,>=2.18.4' h5py==2.8.0rc1 scipy==1.0.1 boto3
-pip3 install nose cpplint==1.3.0 pylint==2.1.1 'numpy<=1.15.2,>=1.8.2' nose-timer 'requests<2.19.0,>=2.18.4' h5py==2.8.0rc1 scipy==1.0.1 boto3
+pip2 install nose cpplint==1.3.0 pylint==1.9.3 'numpy<=1.15.2,>=1.8.2' nose-timer 'requests<2.19.0,>=2.18.4' h5py==2.8.0rc1 scipy==1.0.1 boto3 Cython==0.28.5
+pip3 install nose cpplint==1.3.0 pylint==2.1.1 'numpy<=1.15.2,>=1.8.2' nose-timer 'requests<2.19.0,>=2.18.4' h5py==2.8.0rc1 scipy==1.0.1 boto3 Cython==0.28.5

ci/docker/runtime_functions.sh

@@ -41,6 +41,26 @@ scala_prepare() {
     export MAVEN_OPTS="-Dorg.slf4j.simpleLogger.log.org.apache.maven.cli.transfer.Slf4jMavenTransferListener=warn"
 }
 
+check_cython() {
+    set -ex
+    local python_ver=$1
+    local is_cython_used=$(python${python_ver} <<EOF
+import sys
+import mxnet as mx
+cython_ndarraybase = 'mxnet._cy' + str(sys.version_info.major) + '.ndarray'
+print(mx.nd._internal.NDArrayBase.__module__ == cython_ndarraybase)
+EOF
+)
+
+    if [ "${is_cython_used}" != "True" ]; then
+        echo "ERROR: cython is not used."
+        return 1
+    else
+        echo "NOTE: cython is used."
+        return 0
+    fi 
+}
+
 build_ccache_wrappers() {
     set -ex
 
@@ -370,6 +390,8 @@ build_ubuntu_cpu_openblas() {
         USE_LIBJPEG_TURBO=1           \
         USE_SIGNAL_HANDLER=1          \
         -j$(nproc)
+    make cython PYTHON=python2
+    make cython PYTHON=python3
 }
 
 build_ubuntu_cpu_mkl() {
@@ -682,6 +704,9 @@ build_ubuntu_gpu_cuda91_cudnn7() {
         CUDA_ARCH="$CI_CUDA_COMPUTE_CAPABILITIES" \
         USE_SIGNAL_HANDLER=1                      \
         -j$(nproc)
+
+    make cython PYTHON=python2
+    make cython PYTHON=python3
 }
 
 build_ubuntu_amalgamation() {
@@ -749,6 +774,7 @@ build_ubuntu_gpu_cmake() {
         -DCMAKE_BUILD_TYPE=Release              \
         -DCUDA_ARCH_NAME=Manual                 \
         -DCUDA_ARCH_BIN=$CI_CMAKE_CUDA_ARCH_BIN \
+        -DBUILD_CYTHON_MODULES=1                \
         -G Ninja                                \
         /work/mxnet
 
@@ -769,12 +795,25 @@ sanity_check() {
     nosetests-3.4 tests/tutorials/test_sanity_tutorials.py
 }
 
+unittest_ubuntu_python2_cpu_cython() {
+    set -ex
+    export PYTHONPATH=./python/
+    export MXNET_MKLDNN_DEBUG=1
+    export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
+    export MXNET_ENABLE_CYTHON=1
+    export MXNET_ENFORCE_CYTHON=1
+    check_cython 2
+    nosetests-2.7 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_unittest.xml --verbose tests/python/unittest
+    nosetests-2.7 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_train.xml --verbose tests/python/train
+    nosetests-2.7 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_quantization.xml --verbose tests/python/quantization
+}
 
 unittest_ubuntu_python2_cpu() {
     set -ex
     export PYTHONPATH=./python/
     export MXNET_MKLDNN_DEBUG=1
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
+    export MXNET_ENABLE_CYTHON=0
     nosetests-2.7 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_unittest.xml --verbose tests/python/unittest
     nosetests-2.7 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_train.xml --verbose tests/python/train
     nosetests-2.7 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_quantization.xml --verbose tests/python/quantization
@@ -785,6 +824,7 @@ unittest_ubuntu_python3_cpu() {
     export PYTHONPATH=./python/
     export MXNET_MKLDNN_DEBUG=1  # Ignored if not present
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
+    export MXNET_ENABLE_CYTHON=0
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_unittest.xml --verbose tests/python/unittest
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_quantization.xml --verbose tests/python/quantization
 }
@@ -794,6 +834,7 @@ unittest_ubuntu_python3_cpu_mkldnn() {
     export PYTHONPATH=./python/
     export MXNET_MKLDNN_DEBUG=1  # Ignored if not present
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
+    export MXNET_ENABLE_CYTHON=0
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_unittest.xml --verbose tests/python/unittest
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_mkl.xml --verbose tests/python/mkl
 }
@@ -813,6 +854,19 @@ unittest_ubuntu_python3_gpu() {
     export MXNET_MKLDNN_DEBUG=1 # Ignored if not present
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
     export CUDNN_VERSION=${CUDNN_VERSION:-7.0.3}
+    export MXNET_ENABLE_CYTHON=0
+    nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_gpu.xml --verbose tests/python/gpu
+}
+
+unittest_ubuntu_python3_gpu_cython() {
+    set -ex
+    export PYTHONPATH=./python/
+    export MXNET_MKLDNN_DEBUG=1 # Ignored if not present
+    export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
+    export CUDNN_VERSION=${CUDNN_VERSION:-7.0.3}
+    export MXNET_ENABLE_CYTHON=1
+    export MXNET_ENFORCE_CYTHON=1
+    check_cython 3
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_gpu.xml --verbose tests/python/gpu
 }
 
@@ -821,6 +875,7 @@ unittest_ubuntu_python3_gpu_nocudnn() {
     export PYTHONPATH=./python/
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
     export CUDNN_OFF_TEST_ONLY=true
+    export MXNET_ENABLE_CYTHON=0
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_gpu.xml --verbose tests/python/gpu
 }
 
@@ -830,6 +885,7 @@ unittest_ubuntu_tensorrt_gpu() {
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
     export LD_LIBRARY_PATH=/work/mxnet/lib:$LD_LIBRARY_PATH
     export CUDNN_VERSION=${CUDNN_VERSION:-7.0.3}
+    export MXNET_ENABLE_CYTHON=0
     python tests/python/tensorrt/lenet5_train.py
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_trt_gpu.xml --verbose --nocapture tests/python/tensorrt/
 }
@@ -842,6 +898,7 @@ unittest_ubuntu_python2_quantization_gpu() {
     export MXNET_MKLDNN_DEBUG=1  # Ignored if not present
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
     export CUDNN_VERSION=${CUDNN_VERSION:-7.0.3}
+    export MXNET_ENABLE_CYTHON=0
     nosetests-2.7 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_quantization_gpu.xml --verbose tests/python/quantization_gpu
 }
 
@@ -853,6 +910,7 @@ unittest_ubuntu_python3_quantization_gpu() {
     export MXNET_MKLDNN_DEBUG=1 # Ignored if not present
     export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
     export CUDNN_VERSION=${CUDNN_VERSION:-7.0.3}
+    export MXNET_ENABLE_CYTHON=0
     nosetests-3.4 $NOSE_COVERAGE_ARGUMENTS $NOSE_TIMER_ARGUMENTS --with-xunit --xunit-file nosetests_quantization_gpu.xml --verbose tests/python/quantization_gpu
 }
 

ci/jenkins/Jenkins_steps.groovy

@@ -24,18 +24,20 @@ utils = load('ci/Jenkinsfile_utils.groovy')
 
 // mxnet libraries
 mx_lib = 'lib/libmxnet.so, lib/libmxnet.a, 3rdparty/dmlc-core/libdmlc.a, 3rdparty/tvm/nnvm/lib/libnnvm.a'
+mx_lib_cython = 'lib/libmxnet.so, lib/libmxnet.a, 3rdparty/dmlc-core/libdmlc.a, 3rdparty/tvm/nnvm/lib/libnnvm.a, python/mxnet/_cy2/*.so, python/mxnet/_cy3/*.so'
 
 // Python wheels
 mx_pip = 'build/*.whl'
 
 // mxnet cmake libraries, in cmake builds we do not produce a libnvvm static library by default.
 mx_cmake_lib = 'build/libmxnet.so, build/libmxnet.a, build/3rdparty/dmlc-core/libdmlc.a, build/tests/mxnet_unit_tests, build/3rdparty/openmp/runtime/src/libomp.so'
+mx_cmake_lib_cython = 'build/libmxnet.so, build/libmxnet.a, build/3rdparty/dmlc-core/libdmlc.a, build/tests/mxnet_unit_tests, build/3rdparty/openmp/runtime/src/libomp.so, python/mxnet/_cy2/*.so, python/mxnet/_cy3/*.so'
 // mxnet cmake libraries, in cmake builds we do not produce a libnvvm static library by default.
 mx_cmake_lib_debug = 'build/libmxnet.so, build/libmxnet.a, build/3rdparty/dmlc-core/libdmlc.a, build/tests/mxnet_unit_tests'
 mx_cmake_mkldnn_lib = 'build/libmxnet.so, build/libmxnet.a, build/3rdparty/dmlc-core/libdmlc.a, build/tests/mxnet_unit_tests, build/3rdparty/openmp/runtime/src/libomp.so, build/3rdparty/mkldnn/src/libmkldnn.so.0'
 mx_mkldnn_lib = 'lib/libmxnet.so, lib/libmxnet.a, lib/libiomp5.so, lib/libmkldnn.so.0, lib/libmklml_intel.so, lib/libsparse_matrix.so, 3rdparty/dmlc-core/libdmlc.a, 3rdparty/tvm/nnvm/lib/libnnvm.a'
 mx_tensorrt_lib = 'build/libmxnet.so, lib/libnvonnxparser_runtime.so.0, lib/libnvonnxparser.so.0, lib/libonnx_proto.so, lib/libonnx.so'
-mx_lib_cpp_examples = 'lib/libmxnet.so, lib/libmxnet.a, 3rdparty/dmlc-core/libdmlc.a, 3rdparty/tvm/nnvm/lib/libnnvm.a, 3rdparty/ps-lite/build/libps.a, deps/lib/libprotobuf-lite.a, deps/lib/libzmq.a, build/cpp-package/example/*'
+mx_lib_cpp_examples = 'lib/libmxnet.so, lib/libmxnet.a, 3rdparty/dmlc-core/libdmlc.a, 3rdparty/tvm/nnvm/lib/libnnvm.a, 3rdparty/ps-lite/build/libps.a, deps/lib/libprotobuf-lite.a, deps/lib/libzmq.a, build/cpp-package/example/*, python/mxnet/_cy2/*.so, python/mxnet/_cy3/*.so'
 mx_lib_cpp_examples_cpu = 'build/libmxnet.so, build/cpp-package/example/*'
 
 // Python unittest for CPU
@@ -46,6 +48,12 @@ def python2_ut(docker_container_name) {
   }
 }
 
+def python2_ut_cython(docker_container_name) {
+  timeout(time: max_time, unit: 'MINUTES') {
+    utils.docker_run(docker_container_name, 'unittest_ubuntu_python2_cpu_cython', false)
+  }
+}
+
 // Python 3
 def python3_ut(docker_container_name) {
   timeout(time: max_time, unit: 'MINUTES') {
@@ -89,6 +97,12 @@ def python3_gpu_ut_nocudnn(docker_container_name) {
   }
 }
 
+def python3_gpu_ut_cython(docker_container_name) {
+  timeout(time: max_time, unit: 'MINUTES') {
+    utils.docker_run(docker_container_name, 'unittest_ubuntu_python3_gpu_cython', true)
+  }
+}
+
 //------------------------------------------------------------------------------------------
 
 def compile_unix_cpu_openblas() {
@@ -98,7 +112,7 @@ def compile_unix_cpu_openblas() {
           timeout(time: max_time, unit: 'MINUTES') {
             utils.init_git()
             utils.docker_run('ubuntu_cpu', 'build_ubuntu_cpu_openblas', false)
-            utils.pack_lib('cpu', mx_lib, true)
+            utils.pack_lib('cpu', mx_lib_cython, true)
           }
         }
       }
@@ -224,7 +238,7 @@ def compile_unix_cmake_gpu() {
           timeout(time: max_time, unit: 'MINUTES') {
             utils.init_git()
             utils.docker_run('ubuntu_gpu', 'build_ubuntu_gpu_cmake', false)
-            utils.pack_lib('cmake_gpu', mx_cmake_lib, true)
+            utils.pack_lib('cmake_gpu', mx_cmake_lib_cython, true)
           }
         }
       }
@@ -546,8 +560,8 @@ def test_unix_python2_cpu() {
       node(NODE_LINUX_CPU) {
         ws('workspace/ut-python2-cpu') {
           try {
-            utils.unpack_and_init('cpu', mx_lib, true)
-            python2_ut('ubuntu_cpu')
+            utils.unpack_and_init('cpu', mx_lib_cython, true)
+            python2_ut_cython('ubuntu_cpu')
             utils.publish_test_coverage()
           } finally {
             utils.collect_test_results_unix('nosetests_unittest.xml', 'nosetests_python2_cpu_unittest.xml')
@@ -648,8 +662,14 @@ def test_unix_python3_gpu() {
       node(NODE_LINUX_GPU) {
         ws('workspace/ut-python3-gpu') {
           try {
-            utils.unpack_and_init('gpu', mx_lib, true)
-            python3_gpu_ut('ubuntu_gpu')
+            /*
+             * CMake build with llvm openmp causes a segmentation fault.
+             * We can restore this if the issue is addressed (#12160).
+             *
+             * utils.unpack_and_init('cmake_gpu', mx_cmake_lib_cython, true)
+             */
+            utils.unpack_and_init('gpu', mx_lib_cython, true)
+            python3_gpu_ut_cython('ubuntu_gpu')
             utils.publish_test_coverage()
           } finally {
             utils.collect_test_results_unix('nosetests_gpu.xml', 'nosetests_python3_gpu.xml')

cmake/BuildCythonModules.cmake

@@ -0,0 +1,38 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+function(add_cython_modules python_version)
+  unset(PYTHON_EXECUTABLE CACHE)
+  set(PYTHONINTERP_FOUND FALSE)
+  find_package(PythonInterp ${python_version} EXACT)
+  if(PYTHONINTERP_FOUND)
+    find_program(CYTHON_EXECUTABLE NAMES cython)
+    if(CYTHON_EXECUTABLE)
+      add_custom_command(COMMAND ${CMAKE_COMMAND} POST_BUILD
+                          -E env MXNET_LIBRARY_PATH=${CMAKE_BINARY_DIR}/libmxnet.so
+                          ${PYTHON_EXECUTABLE} setup.py build_ext --inplace --with-cython
+                          TARGET mxnet
+                          WORKING_DIRECTORY "${PROJECT_SOURCE_DIR}/python")
+      message("-- Cython modules for python${python_version} will be built")
+      set(PYTHON${python_version}_FOUND 1 PARENT_SCOPE)
+    else()
+      message(FATAL_ERROR "-- Cython not found")
+    endif()
+  else()
+    set(PYTHON${python_version}_FOUND 0 PARENT_SCOPE)
+  endif()
+endfunction()

docs/faq/env_var.md

@@ -198,6 +198,22 @@ When USE_PROFILER is enabled in Makefile or CMake, the following environments ca
 	- If set to '0', profiler records the events of the symbolic operators.
 	- If set to '1', profiler records the events of all operators.
 
+## Interface between Python and the C API
+
+* MXNET_ENABLE_CYTHON
+  - Values: 0(false), 1(true) ```(default=1)```
+  - If set to 0, MXNet uses the ctypes to interface with the C API.
+  - If set to 1, MXNet tries to use the cython modules for the ndarray and symbol. If it fails, the ctypes is used or an error occurs depending on MXNET_ENFORCE_CYTHON.
+
+* MXNET_ENFORCE_CYTHON
+  - Values: 0(false) or 1(true) ```(default=0)```
+  - This has an effect only if MXNET_ENABLE_CYTHON is 1.
+  - If set to 0, MXNet fallbacks to the ctypes if importing the cython modules fails.
+  - If set to 1, MXNet raises an error if importing the cython modules fails.
+
+If cython modules are used, `mx.nd._internal.NDArrayBase` must be `mxnet._cy3.ndarray.NDArrayBase` for python 3 or `mxnet._cy2.ndarray.NDArrayBase` for python 2.
+If ctypes is used, it must be `mxnet._ctypes.ndarray.NDArrayBase`.
+
 ## Other Environment Variables
 
 * MXNET_GPU_WORKER_NSTREAMS

docs/install/index.md

@@ -1371,7 +1371,16 @@ then running:
   free -m # to verify the swapfile size has been increased
 ```
 
-**Step 2** Install MXNet Python Bindings
+**Step 2** Build cython modules (optional)
+
+```bash
+$ pip install Cython
+$ make cython # You can set the python executable with `PYTHON` flag, e.g., make cython PYTHON=python3
+```
+*MXNet* tries to use the cython modules unless the environment variable `MXNET_ENABLE_CYTHON` is set to `0`. If loading the cython modules fails, the default behavior is falling back to ctypes without any warning. To raise an exception at the failure, set the environment variable `MXNET_ENFORCE_CYTHON` to `1`. See [here](/faq/env_var.html) for more details.
+
+
+**Step 3** Install MXNet Python Bindings
 
 To install Python bindings run the following commands in the MXNet directory:
 

make/config.mk

@@ -214,6 +214,9 @@ EXTRA_OPERATORS =
 # Create C++ interface package
 USE_CPP_PACKAGE = 0
 
+# Python executable. Needed for cython target
+PYTHON = python
+
 #----------------------------
 # plugins
 #----------------------------