ceph/src/boost/libs/python/doc/numpy/tutorial/simple.rst

   1 A simple tutorial on Arrays
   2 ===========================
   3
   4 Let's start with a simple tutorial to create and modify arrays.
   5
   6 Get the necessary headers for numpy components and set up necessary namespaces::
   7
   8         #include <boost/python/numpy.hpp>
   9         #include <iostream>
  10
  11         namespace p = boost::python;
  12         namespace np = boost::python::numpy;
  13
  14 Initialise the Python runtime, and the numpy module. Failure to call these results in segmentation errors::
  15
  16         int main(int argc, char **argv)
  17         {
  18           Py_Initialize();
  19           np::initialize();
  20
  21
  22 Zero filled n-dimensional arrays can be created using the shape and data-type of the array as a parameter. Here, the shape is 3x3 and the datatype is the built-in float type::
  23
  24           p::tuple shape = p::make_tuple(3, 3);
  25           np::dtype dtype = np::dtype::get_builtin<float>();
  26           np::ndarray a = np::zeros(shape, dtype);
  27
  28 You can also create an empty array like this ::
  29
  30         np::ndarray b = np::empty(shape,dtype);
  31
  32 Print the original and reshaped array. The array a which is a list is first converted to a string, and each value in the list is extracted using extract< >::
  33
  34           std::cout << "Original array:\n" << p::extract<char const *>(p::str(a)) << std::endl;
  35
  36           // Reshape the array into a 1D array
  37           a = a.reshape(p::make_tuple(9));
  38           // Print it again.
  39           std::cout << "Reshaped array:\n" << p::extract<char const *>(p::str(a)) << std::endl;
  40         }
  41