Boost is a C++ library that can interface with Python. Download it from http://www.boost.org/users/download/. The latest Boost version at the time of writing was 1.56.0. The easiest but also slowest installation method involves the following commands:
$ ./bootstrap.sh --prefix=/path/to/boost $ ./b2 install
The prefix argument specifies the installation directory. In this example, we will assume that Boost was installed under the user's home directory in a directory called Boost (such as ~/Boost). In this directory, a lib and include directory will be created. For Unix and Linux, it is useful to run the following command:
export LD_LIBRARY_PATH=$HOME/Boost/lib:${LD_LIBRARY_PATH}
On Mac OS X, set the following environment variable:
export DYLD_LIBRARY_PATH=$HOME/Boost/lib
Redefine a rain summation function as given in the boost_rain.cpp file in this book's code bundle:
#include <boost/python.hpp>
double sum_rain(boost::python::list rain, int len) {
double sum = 0.;
for (int i = 0; i < len; i++){
int val = boost::python::extract<int>(rain[i]);
if(val == -1) {
sum += 0.025;
} else {
sum += 0.1 * val;
}
}
return sum;
}
BOOST_PYTHON_MODULE(rain) {
using namespace boost::python;
def("sum_rain", sum_rain);
}The function accepts a Python list and the size of the list. Call the function from Python, as given in the rain_demo.py file in this book's code bundle:
import numpy as np
from rain import sum_rain
rain = np.load('../rain.npy')
print "Boost", sum_rain(rain.astype(int).tolist(), len(rain))
rain = .1 * rain
rain[rain < 0] = .025
print "Numpy", rain.sum()We will automate the development process with the Makefile file in this book's code bundle:
CC = g++
PYLIBPATH = $(shell python-config --exec-prefix)/lib
LIB = -L$(PYLIBPATH) $(shell python-config --libs) -L ${HOME}/Boost/lib -lboost_python
OPTS = $(shell python-config --include) -O2 -I${HOME}/Boost/include
default: rain.so
@python ./rain_demo.py
rain.so: rain.o
$(CC) $(LIB) -Wl,-rpath,$(PYLIBPATH) -shared $< -o $@
rain.o: boost_rain.cpp Makefile
$(CC) $(OPTS) -c $< -o $@
clean:
rm -rf *.so *.o
.PHONY: default cleanFrom the command line, run the following commands:
$ make clean;make
The results are identical as expected:
Boost 85291.55 Numpy 85291.55