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Wrapping C++ code with python (manually)

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.

How to embed Python3 with the standard library

I am attempting to embed Python in an (ultimately multiplatform) C++ app.
It's important that my app contains its own Python implementation (in the same way that blender does), so that it is entirely self-contained. (Else it becomes a configuration minefield).
I have two options:
Attempt to embed Python3 without the standard library (which I have asked here)
Attempt to embed Python3 with the standard library.
What is required for (2)?
With this information I would be able to balance the merits of each approach against the effort required to set it up.
My embedded Python will be for my own use (rather than any userland scripting) -- mainly control flow / game logic. I will need very little from the standard library -- maybe I can whittle that down to 0 by tunnelling back into C++ whenever necessary -- for example if I need a random number, I can create a C++ routine and access that from Python. I have all of that covered.
However, it is starting to look as though even a minimal installation will have to contain some stdlib component(s), which prompts the question: "If I must include some, maybe it is better to include all!"

Since this doesn't really have an answer, I will offer this for posterity. I also do not have access to a Mac, so it may be a little different for you than on Linux. Also, the required dependencies must be installed for this to work, but that is usually easy enough to figure out.
Create a working directory
mkdir ~/embeddedpython
cd ~/embeddedpython
Download the Python source
wget https://www.python.org/ftp/python/3.6.1/Python-3.6.1.tgz
Create an installation directory for Python
mkdir ./installation
Extract the downloaded source files
tar xvf Python-3.6.1.tgz
Enter the newly created source directory
cd Python-3.6.1
Configure Python to install in our installation directory
./configure --prefix="/home/<username>/embeddedpython/installation"
Make and install Python
make && make install
Go back to your working directory
cd ..
Create a new PYTHONHOME directory where the library will reside
mkdir home && mkdir home/lib
Copy the Python library to our new home directory
cp -r ./installation/lib/python3.6 ./home/lib/
Create a new c++ source file (embeddedpython.cpp) with the following code taken from the python documentation, with the exception of the setenv function call.
#include <Python.h>
#include <cstdlib>
int main(int argc, char *argv[])
{
setenv("PYTHONHOME", "./home", 1);
wchar_t *program = Py_DecodeLocale(argv[0], NULL);
if (program == NULL) {
fprintf(stderr, "Fatal error: cannot decode argv[0]\n");
exit(1);
}
Py_SetProgramName(program); /* optional but recommended */
Py_Initialize();
PyRun_SimpleString("from time import time,ctime\n"
"print('Today is', ctime(time()))\n");
if (Py_FinalizeEx() < 0) {
exit(120);
}
PyMem_RawFree(program);
return 0;
}
Compile and run
g++ embeddedpython.cpp -I ./installation/include/python3.6m/ ./installation/lib/libpython3.6m.a -lpthread -ldl -lutil
./a.out
> Today is Fri Apr 14 16:06:54 2017
From here on it is standard embedded python as usual. With this method, the "home" directory must be included in your deployment, and the environment variable PYTHONHOME must be set to point to it before any python related code is executed.

You are looking for Boost.Python!
It's a C++ library which enables seamless interoperability between C++ and the Python programming language and in my opinion this should suffice your need, unless you are trying to achieve something else.
It also has a mechanism for embedding the python interpreter into C++ code and one can refer to this link (URL isn't release specific) to delve into the possibilities.
P.S. I believe less in reinventing the wheel and more into the re-usability.

I suppose that you have already double check how to Embedding Python in Another Application (here you will see something which cover embedding python2 but will be true for python3 also in my opinion)
There is different types of embedding:
Very High Level Embedding
Beyond Very High Level Embedding
Pure Embedding
Embedding Python in C++
As your question is relative to "Embedding Python in C++" you may read this:
It is also possible to embed Python in a C++ program; precisely how
this is done will depend on the details of the C++ system used; in
general you will need to write the main program in C++, and use the
C++ compiler to compile and link your program. There is no need to
recompile Python itself using C++.
As one hand you said "(ultimately multiplatform) C++ app", and in the other hand you have "precisely how this is done will depend on the details of the C++ system used", so may you explain more details of the C++ system used ?
You may also find some tips here relative to the use of pybind11 module or another old page which treat about how to Embed Python and Import Modules in C/C++ (python2.6 but I hope you may found inspiration with)
To conclude:
You'll obviously need development packages for Python in order to have
the Python include directory

How to compile a Python package to a dll

Well, I have a Python package. I need to compile it as dll before distribute it in a way easily importable. How? You may suggest that *.pyc. But I read somewhere any *.pyc can be easily decompiled!
Update:
Follow these:
1) I wrote a python package
2) want to distribute it
3) do NOT want distribute the source
4) *.pyc is decompilable >> source can be extracted!
5) dll is standard

Write everything you want to hide in Cython, and compile it to pyd. That's as close as you can get to making compiled python code.
Also, dll is not a standard, not in Python world. They're not portable, either.

Nowadays a simple solutino exists: use Nuitka compiler as described in Nuitka User Manual
Use Case 2 - Extension Module compilation
If you want to compile a single extension module, all you have to do is this:
python -m nuitka --module some_module.py
The resulting file some_module.so can then be used instead of some_module.py.
You need to compile for each platform you want to support and write some initialization code to import so/pyd file ~~appropriate for given platform/python version etc.~~
[EDIT 2021-12]: Actually in python 3 the proper so/dll is determined automatically based on the file name (if it includes python version and platform - can't find PEP for this feature at the moment but Nuitka creates proper names for compiled modules). So for python 2.7 the library name would be something.pyd or something.so whereas for python 3 this would change to something.cp36-win32.pyd or something.cpython-36m-x86_64-linux-gnu.so (for 32bit python 3.6 on x86).
The result is not DLL as requested but Python-native compiled binary format (it is not bytecode like in pyc files; the so/pyd format cannot be easily decompiled - Nuitka compiles to machine code through C++ translation)
EDIT [2020-01]: The compiled module is prone to evaluation methods using python standard mechanisms - e.g. it can be imported as any other module and get its methods listed etc. To secure implementation from being exposed that way there is more work to be done than just compiling to a binary module.

You can use py2exe.org to convert python scripts into windows executables. Granted this will only work on windows, but it's better then nothing.

You can embed python inside C. The real trick is converting between C values and Python values. Once you've done that, though, making a DLL is pretty straightforward.
However, why do you need to make a dll? Do you need to use this from a non-python program?

Python embedding is supported in CFFI version 1.5, you can create a .dll file which can be used by a Windows C application.

I would also using Cython to generate pyd files, like Dikei wrote.
But if you really want to secure your code, you should better write the important stuff in C++. The best would be to combine both C++ and Python. The idea: you would leave the python code open for adjustments, so that you don't have to compile everything over and over again. That means, you would write the "core" in C++ (which is the most secure solution these days) and use those dll files in your python code. It really depends what kind of tool or program you are building and how you want to execute it. I create mostly an execution file (exe,app) once I finish a tool or a program, but this is more for the end user. This could be done with py2exe and py2app (both 64 bit compatible). If you implement the interpreter, the end user's machine doesn't have to have python installed on the system.
A pyd file is the same like a dll and fully supported inside python. So you can normally import your module. You can find more information about it here.
Using and generating pyd files is the fastest and easiest way to create safe and portable python code.
You could also write real dll files in C++ and import them with ctypes to use them (here a good post and here the python description of how it works)

To expand on the answer by Nick ODell
You must be on Windows for DLLs to work, they are not portable.
However the code below is cross platform and all platforms support run-times so this can be re-compiled for each platform you need it to work on.
Python does not (yet) provide an easy tool to create a dll, however you can do it in C/C++
First you will need a compiler (Windows does not have one by default) notably Cygwin, MinGW or Visual Studio.
A basic knowledge of C is also necessary (since we will be coding mainly in C).
You will also need to include the necessary headers, I will skip this so it does not become horribly long, and will assume everything is set up correctly.
For this demonstration I will print a traditional hello world:
Python code we will be converting to a DLL:
def foo(): print("hello world")
C code:
#include "Python.h" // Includes everything to use the Python-C API
int foo(void); // Declare foo
int foo(void) { // Name of our function in our DLL
Py_Initialize(); // Initialise Python
PyRun_SimpleString("print('hello world')"); // Run the Python commands
return 0; // Finish execution
}
Here is the tutorial for embedding Python. There are a few extra things that should be added here, but for brevity I have left those out.
Compile it and you should have a DLL. :)
That is not all. You will need to distribute whatever dependencies are needed, that will mean the python36.dll run-time and some other components to run the Python script.
My C coding is not perfect, so if anyone can spot any improvements please comment and I will do my best to fix the it.
It might also be possible in C# from this answer How do I call a specific Method from a Python Script in C#?, since C# can create DLLs, and you can call Python functions from C#.

You can use pyinstaller for converting the .py files into executable with all required packages into .dll format.
Step 1. pip install pyinstaller,
step 2. new python file let's name it code.py .
step 3. Write some lines of code i.e print("Hello World")
step 4. Open Command Prompt in the same location and write pyinstaller code.py hit enter. Last Step see in the same location two folders name build, dist will be created. inside dist folder there is folder code and inside that folder there is an exe file code.exe along with required .dll files.

If your only goal is to hide your source code, it is much simpler to just compile your code to an executable(use PyInstaller, for example), and use an module with readable source for communication.
NOTE: You might need more converter functions as shown in this example.
Example:
Module:
import subprocess
import codecs
def _encode_str(str):
encoded=str.encode("utf-32","surrogatepass")
return codecs.encode(encoded,"base64").replace(b"\n",b"")
def _decode_str(b64):
return codecs.decode(b64,"base64").decode("utf-32","surrogatepass")
def strlen(s:str):#return length of str;int
proc=subprocess.Popen(["path_to_your_exe.exe","strlen",_encode_str(str).decode("ascii")],stdout=subprocess.PIPE)
return int(proc.stdout.read())
def random_char_from_string(str):
proc=subprocess.Popen(["path_to_your_exe.exe","randchr",_encode_str(str).decode("ascii")],stdout=subprocess.PIPE)
return _decode_str(proc.stdout.read())
Executable:
import sys
import codecs
import random
def _encode_str(str):
encoded=str.encode("utf-32","surrogatepass")
return codecs.encode(encoded,"base64").replace(b"\n",b"")
def _decode_str(b64):
return codecs.decode(b64,"base64").decode("utf-32","surrogatepass")
command=sys.argv[1]
if command=="strlen":
s=_decode_str(sys.argv[2].encode("ascii"))
print(len(str))
if command=="randchr":
s_decode_str(sys.argv[2].encode("ascii"))
print(_encode_str(random.choice(s)).decode("ascii"))
You might also want to think about compiling different executables for different platforms, if your package isn't a windows-only package anyways.

This is my idea, it might work. I don't know, if that work or not.
1.Create your *.py files.
2.Rename them into *.pyx
3.Convert them into *.c files using Cython
4.Compile *.c into *.dll files.
But I don't recommend you because it won't work on any other platforms, except Windows.

Grab Visual Studio Express and IronPython and do it that way? You'll be in Python 2.7.6 world though.

Is it possible to compile c code using python?

I want to build a python program that get as input a path to .c file and then it compile its.
The program will output OK to the screen if the compilation is sucessful, and BAD otherwise.
I'm been trying to google it, but could not find anything. I've been also trying to run cmd within python with an argument of the compiling program but it didn't work.
To clarify - I've already got a very specific compiler in my machine which I want to run. I dont want python to act as a compiler. Just get a code, run my compiler over it, and see what's the answer.
It should work on Linux server with python 2.4.
Thanks

You can compile C code using only the standard library, and it will work on every platform and with every Python version (assuming you actually have a C compiler available). Check out the distutils.ccompiler module which Python uses to compile C extension modules. A simple example:
// main.c
#include <stdio.h>
int main() {
printf("Hello world!\n");
return(0);
}
Compilation script:
# build.py
from distutils.ccompiler import new_compiler
if __name__ == '__main__':
compiler = new_compiler()
compiler.compile(['main.c'])
compiler.link_executable(['main.o'], 'main')
Everything else (include paths, library paths, custom flags or link args or macros) can be passed via various configuration options. Check out the above link to the module documentation for more info.

Sure, why not? Of course, you'd need GCC installed (or llvm) so you have something to compile with. You can just use os.system, or any of the other ways for calling an external program.
Of course, you're probably better off looking at something like SCons, which already exists to solve this problem.
Plus, to answer the question actually asked, there's nothing that would prevent you from writing a compiler/assembler/linker in python, they're just programs like anything else. Performance probably wouldn't be very good though.

The following steps should do the trick:
Get PLY. Python Lex and Yacc. http://www.dabeaz.com/ply/
Find a Yacc/Lex configuration for C. http://www.lysator.liu.se/c/ANSI-C-grammar-y.html
Tweak PLY to use the C language rules you found.
Run. You are "compiling" C code -- checking the syntax.

If I understood you clearly, you just want to run compiler with some arguments from python?
In this case, you can just to use os.system. http://docs.python.org/library/os.html#os.system
Or better way is module "subprocess". http://docs.python.org/library/subprocess.html#module-subprocess

How to hide console window on Windows when using scons-qt4 plugin?

When I'm building on Windows with scons-qt4 plugin, my application always opens a console window, even though it has its own windows. With QMake, you could force application to do the same by adding CONFIG += console or something similar, but the default behaviour is to suppress it. QMake can handle it - I'm sure scons can, too.
The only way I see so far to solve this problem would be to use #ifdef around int main():
#ifdef WIN32
int WinMain (int _argc, char **_argv)
#else
int main (int _argc, char **_argv)
#endif
But that's just abominable!

So, it seems, my question was almost already answered here. Now, applied to scons, these two lines did it for me:
if (env ['PLATFORM'] == 'win32'):
env.Append (LINKFLAGS = ['-Wl,-subsystem,windows'])
Also, kind thanks to the folks on the [scons-users] mailing list. In particular, David Van Maren pointed out that:
You might look for whether you are
linking against the qtmain library.
The latest Qt documentation only says
this about it:
--------------- The qtmain Library
qtmain is a helper library that
enables the developer to write a
cross-platform main() function on
Windows and on the Symbian platform.
If you do not use qmake or other build
tools such as CMake, then you need to
link against theqtmain library.
It may not be related, but I think
that once I added it to the link, the
bogus console disappeared for our Qt
gui applications.
This may be another way to solve the problem, for example, when program is compiled with other tools than GCC + MinGW.