I have script in Python containing several functions, and one Callback (when event occurs).
I would like to release some "package" from my script , which could be importable and usable for other users.
Lets say: Some one can use it for creating GUI app in JAVA, another it will incorporate to his own C++ Gui app, and someone just will call my functions from another Python script.
Can you point me to right direction please?
Thanks.
So you want to be able to call Python functions from Python, Java and C++?
The Python case is just a matter of importing your module.
To call Python functions from Java, try Jython: https://www.jython.org/index.html
To call Python functions from C++, use the Python header files and this approach https://docs.python.org/3/extending/embedding.html. Alternatively, you can use Boost.Python: http://www.boost.org/doc/libs/release/libs/python/doc/index.html
Calling one language from another can be quite a tricky thing. An approach that would work in all languages and avoid major headaches would be to expose a proper public interface (command-line, http, etc) and consume this interface in the other languages.
Other references:
Calling Python in Java?
Calling python from a c++ program for distribution
Related
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 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'm designing musical training games using JUCE -- a multiplatform C++ framework that allows me to code audio/visuals close to the wire.
However, I have coded my gameplay (control flow / data-processing) in Python -- it is complex and I wish to keep changing it so I can experiment with different gameplays. Python is ideal for this kind of rapid prototyping work.
So I would like my (platform independent, so Win/OSX/Lin/iOS/And) C++ to start up a Python runtime, feed it a .py file, and then call various functions in that .py. Also I would like to be able to call back to the C++ code from the .py.
Here is the relevant official Python documentation: https://docs.python.org/2/extending/extending.html
And here is a CodeProject article: http://www.codeproject.com/Articles/11805/Embedding-Python-in-C-C-Part-I
However, neither of them seem to address the issue of multiplatform.
The technique seems to be to link with the library libpython.a, and #include which contains the various functions for starting up the runtime environment, loading scripts, executing python-code, etc.
But surely this libpython.a would need to be compiled separately per platform? If so, this wouldn't be a very clean solution, so could I instead add the Python source code to my project and get it to compile the .a?
How can I go about doing this?
EDIT: https://wiki.python.org/moin/boost.python/EmbeddingPython
EDIT2: I'm pretty sure trying to bring in the full CPython source code is overkill here -- someone must have made some stripped down Python implementation in C/C++ that doesn't support any system-calls/multithreading/fancy-stuff -- just works through Python syntax line by line. Looking thru https://wiki.python.org/moin/PythonImplementations but I can't see an obvious candidate.
EDIT3: https://github.com/micropython/micropython should be added to that last page, but still it doesn't look like it is what I'm after
There's an entire chapter of the Python docs that explain the different approaches you can take embedding a Python interpreter into another app.
Embedding Python is similar to extending it, but not quite. The
difference is that when you extend Python, the main program of the
application is still the Python interpreter, while if you embed
Python, the main program may have nothing to do with Python — instead,
some parts of the application occasionally call the Python interpreter
to run some Python code.
So if you are embedding Python, you are providing your own main
program. One of the things this main program has to do is initialize
the Python interpreter. At the very least, you have to call the
function Py_Initialize(). There are optional calls to pass command
line arguments to Python. Then later you can call the interpreter from
any part of the application.
There are several different ways to call the interpreter: you can pass
a string containing Python statements to PyRun_SimpleString(), or you
can pass a stdio file pointer and a file name (for identification in
error messages only) to PyRun_SimpleFile(). You can also call the
lower-level operations described in the previous chapters to construct
and use Python objects.
A simple demo of embedding Python can be found in the directory
Demo/embed/ of the source distribution.
I recently decided to create a project that mixes C++ with Python, thus getting the best of both worlds. My idea was to do rapid prototyping of classes and functions in Python for obvious reasons, but still being able to call C++ code within Python (for obvious reasons as well). So instead of embedding Python in the C++ framework, I suggest you do the opposite: embed your C++ framework into a Python project. In order to do so, you just have to write very simple interface files and let Swig take care of the interfacing part.
If you want to start from scratch, there's a nice tool called cookiecutter that can be used to generate a project templates. You can choose either the cookiecutter-pypackage, or the cookiecutter-pylibrary, the latter improving over the former as described here. Interestingly, you can also use the cookiecutter code to generate the structure of a C++ project. This empty project uses the CMake build system, which IMHO is the best framework for developing platform independent C++ code. I then had to decide on the directory structure for this mixed project, so one of my previous posts describes this in detail. Good luck!
I'm using SWIG to embed Python into my C++ application, and to extend it as well, i.e. access my C++ API in Python outside my application. SWIG and Python are multi-platform, so that is not really an issue. One of the main advantage of SWIG is that it can generate bindings for a lot of languages. There are also a lot of C++ code wrappers that could be used, for example boost.python or cython.
Check these links on SO:
Extending python - to swig, not to swig or Cython
Exposing a C++ API to Python
Or you can go the hard way and use plain Python/C API.
I have an executable (face recognition) written by one of our programmers who's no longer with us. It takes a commandline argument and prints the result to STDOUT like this.
I need to be able to use this in Python but performance is important so I'm not sure if I should just use subprocess. I need to capture the output of the program so is it a better idea to modify the code to make it a C++ library instead and write a wrapper for it in Python? How would that impact performance compared to using subprocess?
I have looked into the Python docs for running C code and found this but the answer here is different. The second method does not even use Python.h so I'm a little confused. What's the best way to do what I need when performance is important?
At first I have to tell you I think subprocess method and running external application and reading output from STD output would be slow and unreliable. I won't recommend that method.
Instead, here is some suggestions:
You can create a Python extension in C or C++, you can find a lot of resources online about it. So you can convert your current code to Python extension format and just use Python extension skeleton template, integrate your functions and code in it and you'll have a python extension, simply you'll be able to call it's functions from Python code. See: http://docs.python.org/2/extending/index.html
Convert your current C++ code directly into a DLL and exports functions of your code you want to call from python if you are in Windows or simply convert it to a shared library if you are using Linux. It will be compiled to .so . Then you can call functions as an external library in your Python code. Example with explanation: http://www.linuxforu.com/2010/05/extending-python-via-shared-libraries/
I've never tried them, but it seems these projects can help you with what you want:
http://sourceforge.net/projects/pygccxml/?source=dlp
https://code.google.com/p/pybindgen/
http://www.cython.org/
I know that it is possible to write bash extension modules (loadable builtins) on C or lua (see luabash), but is it possible on Python/Cython? Is there any projects that make steps in this direction?
The way you would probably do this is start out with a C library which includes the appropriate exported functions, then within the exported function load and run the python interpreter, run your python code, then tear down the python interpreter.
You can see how to load the python interpreter into a C program/library here:
http://docs.python.org/extending/embedding.html
http://docs.python.org/extending/extending.html#calling-python-functions-from-c
http://www.linuxjournal.com/article/8497
If you do this a lot, then it may be simpler to write a single generic handler when you can use with multiple different python scripts.
I used Bash examples and the linked resources #tylerl mentioned to make bashpy. It's a proof of concept and currently lacks support for both passing variables and calling functions. So not very useful yet, but maybe it can help someone ending up here.