I need to access data via USB from a beam profiler. I've tried using the USB module in python to access it, but unfortunately the company who makes this device "does not support development in Python". The project I am working on is to eventually create a GUI (via Python) to automate a motor and pull data from the device. So it has to be done in Python, or I'm going to have to discard the first half of the code and redo it in C++.
I think the reason the device can only interface with C/C++ is because of the header and library files that come with the driver download.
I've looked at Cython but am still very unsure how it can help me. I'm just trying to access the header files for the driver in python and somehow execute the C commands in python.
BTW I am using Anaconda (if that matters).
Thank-you for any clarification and help!
Check out boost.python
Here is an intro:
The Boost Python Library is a framework for interfacing Python and
C++. It allows you to quickly and seamlessly expose C++ classes
functions and objects to Python, and vice-versa, using no special
tools -- just your C++ compiler. It is designed to wrap C++ interfaces
non-intrusively, so that you should not have to change the C++ code at
all in order to wrap it, making Boost.Python ideal for exposing
3rd-party libraries to Python. The library's use of advanced
metaprogramming techniques simplifies its syntax for users, so that
wrapping code takes on the look of a kind of declarative interface
definition language (IDL).
It includes support for:
References and Pointers
Globally Registered Type Coercions
Automatic Cross-Module Type Conversions
Efficient Function Overloading
C++ to Python Exception Translation
Default Arguments
Keyword Arguments
Manipulating Python objects in C++
Exporting C++ Iterators as Python Iterators
Documentation Strings
and many more.
I have a main file(main.cpp) and a header file(nodes.hpp). The main file takes N(any positive integer) as input argument and by using the functions of header file it gives output say 'x & y' (both double).
Note:
Both main and header files are written in C++.
Both main and header files instead of using data structues as arrays,vectors, make use of Eigen Library.
I have to write a python wrapper for them, I have working knowledge of python but have never used any wrapper.
Can anybody please refer or give some notes about using python wrpper for such code?
Here are your options:
You can use ctypes, and I consider this the cleanest solution, because you convert your program to a shared library that can be called by any other software, not only Python. You, though, have to write a C-interface for your program yourself.
You can use Python C-Extension, and I consider this the worst solution, because it's very low level, and prone to memory leaks, and costs lots of time to implement one function, and is Python-version dependent. Basically this is good to start a Python interpreter inside your C++. You can create PyObjects (which is the main building block of any Python type) and deal with them insdie C/C++.
You can use SWIG, where it automatically creates the the interface that you have to create with ctypes through an interface file that you define. People say it's very good, but the documentation is not as good.
You can use Boost.Python, which is good, but it has a very ugly build system with bjam. If you can manage to bypass that, then it's even better than ctypes. I'm a big boost fan, but bjam is why I don't use this.
What I do typically is ctypes. I trust it because it emphasizes the single-reponsibility principle. The library has a job that's separate from the interface (the C-interface), which is also separate from your Python script that uses that interface and exposes "the easy functionality" to the user.
Use Boost.Python. Here is my tutorial, previously on SO Docs.
Using Boost.Python
Things are easy when you have to use a C++ library in a Python project. Just you can use Boost.
First of all here is a list of components you need:
A CMakeList.txt file, because you're going to use CMake.
The C++ files of the C++ project.
The python file - this is your python project.
Let's start with a small C++ file. Our C++ project has only one method which returns some string "This is the first try". Call it CppProject.cpp
char const *firstMethod() {
return "This is the first try.";
}
BOOST_PYTHON_MODULE(CppProject) {
boost::python::def("getTryString", firstMethod); // boost::python is the namespace
}
Have a CMakeLists.txt file a below:
cmake_minimum_required(VERSION 2.8.3)
FIND_PACKAGE(PythonInterp)
FIND_PACKAGE(PythonLibs)
FIND_PACKAGE(Boost COMPONENTS python)
INCLUDE_DIRECTORIES(${Boost_INCLUDE_DIRS} ${PYTHON_INCLUDE_DIRS})
PYTHON_ADD_MODULE(NativeLib CppProject)
FILE(COPY MyProject.py DESTINATION .) # See the whole tutorial to understand this line
By this part of the tutorial everything is so easy. you can import the library and call method in your python project. Call your python project MyProject.py.
import NativeLib
print (NativeLib.getTryString)
In order to run your project follow the instructions below:
Create a directory with the name build.
Enter into that directory.
Give the command cmake -DCMAKE_BUILD_TYPE=Release ..
make
python MyProject.py. Now, you have to see the string which the method in your C++ project returns.
Another tool for C++ wrapper generation is CLIF. Released in 2017, Google uses this for most everything these days. We no longer allow new SWIG wrappers to be written for Python internally.
It is built on top of Clang for the C++ parsing and requires relatively idiomatic modern C++ API use (unsurprisingly following Google's Style Guide) rather than any attempt to allow you to shoot yourself in the foot via SWIG's "support everything poorly" approach.
Try with official documentation:
https://docs.python.org/2/extending/extending.html
this link will provide you simple example of how to include a cpp module and use it from the python interpreter, or if this is possible try with Cython: http://cython.org/
Cython will allow you to write C-like, Python-like code which will be translated to CPP compiled and then will be easily accessible from the Python.
You can use Boost.Python
or go with the Python native interface
I would recommend Boost.Python if you already have Boost set up.
I am trying to create an application in which the GUI is programmed in Python (Tkinter) and I have a library in C++ that I want to interface with this GUI code. (Please, no comments on why the GUI and the application library are in separate languages).
One approach that immediately comes to mind is to compile the C++ library into an executable and write python wrappers that call this executable ( via system() ) with specific arguments and consume the output.
I am not sure what the performance implications are for such an implementation. Also I do not want to change the library into Python. Any better suggestions or comments on the approach?
There are several ways for doing this. One obvious way was already stated by chis. Another good way of interfacing C++ with Python is by using swig. It all comes down how complex your structures / classes are.
So the C++ code is going to be a module in python and can be called by the interface as any other python function.
I do automation and currently automating an application made with QT (C++).
I use Squish to do this using Python scripting language.
Can someone explain me exactly how a Python variable can be assigned a C++ Object?
Do you need to refer C++ built-in types (int, long, char, wchar_t, etc.) and arrays in Python code? If so you need to use ctypes Python package. Here is an example of calling C++ dll function from Python. If you need to send Window message (like WM_CLICK) take a look at ctypes.Structure class. There are some examples of C structures declared in Python code.
EDIT: Currently I know 2 open source projects about QT GUI automation.
funq
GammaRay
Also it's possible to build and run QT app with accessibility features for Windows UIA and Linux AT-SPI.
I'm working in an embedded Linux environment and I have some Python code which I would like to use. My Python code is just doing some math, not using any library other than Numpy and the common ones.
Is there any way to build up a library that I can call from C or C++ code?
Embedding the CPython interpreter into a C or C++ program is actually pretty straightforward.
The official documentation has some complete examples.
Also, check out SWIG and Boost.Python.