numpy c api import fixed

Author: JohanMabille

docs/source/basic_usage.rst

@@ -17,6 +17,7 @@ Example 1: Use an algorithm of the C++ library on a numpy array inplace
     #include <numeric>                        // Standard library import for std::accumulate
     #include "pybind11/pybind11.h"            // Pybind11 import to define Python bindings
     #include "xtensor/xmath.hpp"              // xtensor import for the C++ universal functions
+    #define FORCE_IMPORT_ARRAY                // numpy C api loading
     #include "xtensor-python/pyarray.hpp"     // Numpy bindings
 
     double sum_of_sines(xt::pyarray<double> &m)
@@ -28,6 +29,7 @@ Example 1: Use an algorithm of the C++ library on a numpy array inplace
 
     PYBIND11_PLUGIN(xtensor_python_test)
     {
+        import_array() //this is actually a macro
         pybind11::module m("xtensor_python_test", "Test module for xtensor python bindings");
 
         m.def("sum_of_sines", sum_of_sines,
@@ -64,6 +66,7 @@ Example 2: Create a universal function from a C++ scalar function
 .. code::
 
     #include "pybind11/pybind11.h"
+    #define FORCE_IMPORT_ARRAY
     #include "xtensor-python/pyvectorize.hpp"
     #include <numeric>
     #include <cmath>
@@ -77,6 +80,7 @@ Example 2: Create a universal function from a C++ scalar function
 
     PYBIND11_PLUGIN(xtensor_python_test)
     {
+        import_array()
         py::module m("xtensor_python_test", "Test module for xtensor python bindings");
 
         m.def("vectorized_func", xt::pyvectorize(scalar_func), "");

docs/source/index.rst

@@ -61,6 +61,7 @@ This software is licensed under the BSD-3-Clause license. See the LICENSE file f
 
    basic_usage
    array_tensor
+   numpy_capi
    cookie_cutter
 
 .. toctree::

docs/source/numpy_capi.rst

@@ -0,0 +1,62 @@
+.. Copyright (c) 2016, Johan Mabille and Sylvain Corlay
+
+   Distributed under the terms of the BSD 3-Clause License.
+
+   The full license is in the file LICENSE, distributed with this software.
+
+Importing numpy C API
+=====================
+
+Importing the C API module of numpy requires more code than just including a header. ``xtensor-python`` simplifies a lot
+this import, however some actions are still required in the user code.
+
+Extension module with a single file
+-----------------------------------
+
+When writing an extension module that is self-contained in a single file, its author should pay attention to the following
+points:
+
+- ``FORCE_IMPORT_ARRAY`` must be defined before including any header of ``xtensor-python``.
+- ``import_array()`` must be called in the function initializing the module.
+
+Thus the basic skeleton of the module looks like:
+
+.. code::
+
+    #include "pybind11/pybind11.h"
+    #define FORCE_IMPORT_ARRAY
+    #include "xgtensor-python/pyarray.hpp"
+
+    PYBIND11_PLUGIN(plugin_name)
+    {
+        import_array()
+        pybind11::module m(//...
+        //...
+        return m.ptr();
+    }
+
+
+Extension module with multiple files
+------------------------------------
+
+If the extension module contain many source files that include ``xtensor-python`` header files, the previous points are still
+required. However, the source files that don't contain the initializing code of the module can directly include ``xtensor-python``
+header files.
+
+
+Using other extension modules
+-----------------------------
+
+Including an header of ``xtensor-python`` actually defines ``PY_ARRAY_UNIQUE_SYMBOL`` to ``xtensor_python_ARRAY_API``. This might
+be problematic if you import another library that defines its own ``PY_ARRAY_UNIQUE_SYMBOL``, or if you define yours. If so,
+you can override the behavior of ``xtensor-python`` by explicitly defining ``PY_ARRAY_UNIQUE_SYMBOL`` prior to including any
+``stenxor-python`` header:
+
+.. code::
+
+    // in every source file
+    #define PY_ARRAY_UNIQUE_SYMBOL my_uniqe_array_api
+    #include "xtensor-python/pyarray.hpp"
+
+
+

include/xtensor-python/pycontainer.hpp

@@ -17,38 +17,23 @@
 #include "pybind11/common.h"
 #include "pybind11/complex.h"
 
+#ifndef FORCE_IMPORT_ARRAY
+#define NO_IMPORT_ARRAY
+#endif
+#ifndef PY_ARRAY_UNIQUE_SYMBOL
+#define PY_ARRAY_UNIQUE_SYMBOL xtensor_python_ARRAY_API
+#endif
 #define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
 #include "numpy/arrayobject.h"
 
 #include "xtensor/xcontainer.hpp"
 
 namespace xt
 {
-    static bool is_numpy_imported = false;
-
-    class numpy_import
-    {
-    protected:
-
-        inline numpy_import()
-        {
-            if (!is_numpy_imported)
-            {
-                _import_array();
-                is_numpy_imported = true;
-            }
-        }
-
-        numpy_import(const numpy_import&) = default;
-        numpy_import(numpy_import&&) = default;
-        numpy_import& operator=(const numpy_import&) = default;
-        numpy_import& operator=(numpy_import&&) = default;
-    };
 
     template <class D>
     class pycontainer : public pybind11::object,
-                        public xcontainer<D>,
-                        private numpy_import
+                        public xcontainer<D>
     {
     public:
 

test/main.cpp

@@ -8,12 +8,19 @@
 
 #include <Python.h>
 
+#include "pybind11/numpy.h"
+
+#define FORCE_IMPORT_ARRAY
+#include "xtensor-python/pyarray.hpp"
+
 #include "gtest/gtest.h"
+#include <iostream>
 
 int main(int argc, char* argv[])
 {
     // Initialize all the things (google-test and Python interpreter)
     Py_Initialize();
+    import_array()
     ::testing::InitGoogleTest(&argc, argv);
 
     // Run test suite

test/test_pyarray.cpp

@@ -7,9 +7,7 @@
 ****************************************************************************/
 
 #include "gtest/gtest.h"
-
 #include "test_common.hpp"
-
 #include "xtensor-python/pyarray.hpp"
 
 namespace xt

test/test_pytensor.cpp

@@ -7,9 +7,7 @@
 ****************************************************************************/
 
 #include "gtest/gtest.h"
-
 #include "test_common.hpp"
-
 #include "xtensor-python/pytensor.hpp"
 
 namespace xt

test_python/main.cpp

@@ -10,7 +10,7 @@
 
 #include "xtensor/xmath.hpp"
 #include "xtensor/xarray.hpp"
-
+#define FORCE_IMPORT_ARRAY
 #include "xtensor-python/pyarray.hpp"
 #include "xtensor-python/pyvectorize.hpp"
 
@@ -51,6 +51,7 @@ int add(int i, int j)
 
 PYBIND11_PLUGIN(xtensor_python_test)
 {
+    import_array()
     py::module m("xtensor_python_test", "Test module for xtensor python bindings");
 
     m.def("example1", example1);