In this final part of the series I’m going to look at one further way we can use Boost.Python to help when using a C++ class within Python.
In the previous part we built a wrapper for a C++ class, exposing a number of class methods to Python.
However, in Python, it’s quite typical for a class to use properties as well as methods.
So to begin – let’s take a moment to look at properties within the context of classes in Python.
For example, if we had a Python class which looks like this:
def __init__ (self):
self._data = None
def set_data(self, data):
self._data = data
We could then use it, something like this:
s = example.simple()
Whilst this works, we might reasonably say that the necessity to use getter and setter functions directly is not especially Pythonic – as it’s not how most built-in objects behave.
Instead we’d expect to be able to use it more like this:
s.data = 7
We can do exactly this; if we use properties…
Continue reading “Advanced C++ / Python integration with Boost.Python (Part 3)”
Last time we looked at how to use Boost.Python to wrap a very simple piece of C++ code. This time we’re going to take that one step further along, and do the same thing for a more complex C++ example – which includes a C++ Class.
For the purposes of this example – let us assume that we have a “legacy” C++ class (i.e. one that we’re not going to change): which looks something like this:
unsigned char* exporter();
void set_data(uint8_t, uint8_t, uint8_t);
void importer(unsigned char*, int);
This (deliberately, slightly contrived) class has three methods (and a constructor). We can set the three 8-bit unsigned integers (
uint8_t) directly using the
set_data() method; we can print the data to the screen; or we can either import from or export to an
In order to be able to use the importer & exporter methods with Python (via Boost.Python) we’ll need to further wrap these – as Boost.Python won’t let us use
unsigned char* directly.
Continue reading “Advanced C++ / Python integration with Boost.Python (Part 2)”
In a previous post, I described how you could use the ctypes Python library to import a C++ class to make it usable from within Python. There is however, another way to do this; and that’s by using Boost.Python (which as the name suggests is a part of the Boost C++ library suite).
Whilst this method makes our code on the C++ side slightly more complicated; it significantly simplifies the Python code – and it let’s us use some more powerful features.
To begin let’s start with a simple example.
char const* greet()
return "hello, world";
std::string multi_bob(int n)
std::string name = "Bob";
std::string r = "";
for (int i=0;i<n;i++)
r += name;
using namespace boost::python;
Everything above the
BOOST_PYTHON_MODULE line is perfectly ordinary C++ code. The clever bit comes in when we call the
BOOST_PYTHON_MODULE macro (which is defined within the Boost.Python header)…
In this case we’re creating a Python module – with two methods: one based on our very simple
greet() function (which we’re also going to call
greet); and one based on the more complex
multi_bob(int) function. Note that for this second function, to show the fact that the linkage between the C++ & Python code can be very flexible, we give it a different name on the Python side. Also note that we don’t need to tell the macro about the signature of the function as this is handled for us by Boost.Python.
Continue reading “Advanced C++ / Python integration with Boost.Python”