I'm currently working on a project with a separate cli and gui. The gui part is written in C++ to keep the exectuable small. I compiled my python program with pyinstaller and need to call some functions from the C++ program.
Python part:
import configparser
def getconfig() -> list:
config = configparser.ConfigParser()
config.read("config.ini")
section1 = config["general"]
section2 = section["section2"]
return [section1, section2] #should be a list of dict?
Compiling it via pyinstaller --onefile --clean myprogram.py
What i would like to do in C++ is :
//please correct me if this is the wrong type,
//i know i probably need to do a bit of parsing between python and C++ types
std::vector<std::unordered_map<std::string, std::string>> > = myprogram.getconfig()
I just don't want to do the config parsing in C++ again, or would you recommend this as it's probably easier to call the compiled python binary?
This program just needs to run on linux, windows is not necessary.
If you are only planning to run on POSIX-compatible systems (ie. GNU/Linux), you could spawn a new process to run the Python script, e.g. using the C function exec. Example:
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
int main()
{
char* args[] = { "pythonscript.py", NULL };
int t = execv("pythonscript.py", args);
if(t < 0) printf("%s\n", strerror(errno));
return 0;
}
And then in pythonscript.py:
#!/usr/bin/python3
print("hello, world!")
This trick works with bash scripts as well.
The script must be executable though, so remember to run chmod +x pythonscript.py.
EDIT:
You will likely need to use pipes or other mechanisms for inter-process communication. (this is not my expertise!)
Related
I'm trying to read a string list output from a Python script, in order to pass it to a JUCE MainComponent (written in C++).
The code is the following (which is a starting one, just to test the pybind library):
#include <pybind11/embed.h>
#include <pybind11/pybind11.h>
namespace py = pybind11;
MainComponent::MainComponent()
{
auto math = py::module::import("math");
auto resultobj = math.attr("sqrt")(2);
double result = resultobj.cast<double>();
}
However, I always encounter the following error:
_PyRuntime.gc.**generation0** was nullptr.
Any suggestions? Thanks in advance
You have to first initialize the Python interpreter, like this:
MainComponent::MainComponent()
{
py::scoped_interpreter guard{};
auto math = py::module::import("math");
auto resultobj = math.attr("sqrt")(2);
double result = resultobj.cast<double>();
}
You also have to link with the needed python libraries. In CMake, this means adding
target_link_libraries(your_target PRIVATE pybind11::embed)
to your CMakeLists.txt file.
Essentially, on the C++ side I have a container that holds a certain type of function. Now I would like to expose this container to python with the possibility for the users to provide their own python functions.
The simplest example would look like this:
#include "pybind/common/Common.h"
using CppFunc = std::function< int (int) >;
PYBIND11_MODULE( test, m )
{
m.def("addFunc", [](const pybind11::function& f){
static std::vector<CppFunc> vec{};
vec.push_back(f.cast<CppFunc>());
});
}
Then in python I would like to just do something like this.
import test
def myFunc(number):
return number+1
test.addFunc(myFunc)
Interestingly enough, this works fine. However, if I run the script with "python script.py" it runs through and then never terminates. In an interactive console, the same code works fine until you try to close the console: the process gets stuck.
How can I safely store this python function in the C++ container?
static std::vector<CppFunc> vec{} stores references to python objects (user functions) which never get released due to static storage, therefore interpreter cannot terminate.
To ensure interpreter termination you can call a cleanup function at module termination:
#include "pybind11/pybind11.h"
#include "pybind11/functional.h"
namespace py = pybind11;
using CppFunc = std::function< int (int) >;
PYBIND11_MODULE( test , m )
{
static std::vector<CppFunc> vec{};
m.def("addFunc", [](CppFunc f){
vec.push_back(std::move(f));
});
m.add_object("_cleanup", py::capsule([]{ vec.clear(); }));
}
See doc for more details: https://pybind11.readthedocs.io/en/stable/advanced/misc.html#module-destructors
Following is the c++ code which I want to import.
#include <boost/python.hpp>
#include <string>
/*
* This is the C++ function we write and want to expose to Python.
*/
const std::string hello() {
return std::string("hello, zoo");
}
/*
* This is a macro Boost.Python provides to signify a Python extension module.
*/
BOOST_PYTHON_MODULE(zoo) {
// An established convention for using boost.python.
using namespace boost::python;
// Expose the function hello().
def("hello", hello);
}
The following code is python script.
import zoo # In zoo.cpp we expose hello() function, and it now exists
in the zoo module.
assert 'hello' in dir(zoo) # zoo.hello is a callable.
assert callable(zoo.hello) # Call the C++ hello() function from Python.
print zoo.hello()
When I try to run the script, I am not getting "hello, zoo" at the terminal as output. Where am I making the mistake?
Following is the error message I am getting:
import: not authorized zoo' # error/constitute.c/WriteImage/1028.
./visit_zoo.py: line 3: syntax error near unexpected token('
./visit_zoo.py: line 3: `assert 'hello' in dir(zoo)'
Aren't you forgetting to indicate the script should be run by Python, as I did?
You can either include the python executable in the header of your script file:
#!/usr/bin/env python2
and make the file executable or call the script with Python:
$ python <filename>
I'm a regular C user, but pretty new to Python.
I have a library written in C for performing calculations that I'm trying to make callable from a Python script. The library needs some user defined routines, for which I am trying to allow the use of Python scripts.
I am running into a problem which demonstrates to me that I do not understand something very fundamental. Here is the code for a simple program I cannot get to run. It should print to the screen the result of 7 (2+5).
The Python script test.py is called first. It loads ctypes and the library libfoo.so, and calls the C routine c_do_work:
from ctypes import cdll
lib = cdll.LoadLibrary('./libfoo.so')
print "Python 1: Going in..."
lib.c_do_work(2,5)
The C function c_do_work is defined in the library libfoo.so, which has the single module test.c. This routine should run the Python script my_func.py, which defines the function find_sum. A Python interpreter is initialized here:
//gcc test.c -I/usr/include/python2.7/ -L/usr/lib/python2.7/ -lpython2.7 -lm -fPIC -c
//gcc -shared -Wl,-soname,libfoo.so -o libfoo.so test.o
#include <Python.h>
#include <stdio.h>
#include <stdlib.h>
void c_do_work(int a,int b)
{
Py_Initialize();
PyObject* main_module = PyImport_AddModule("__main__");
PyObject* main_dict = PyModule_GetDict(main_module);
FILE* file_1 = fopen("my_func.py", "r");
PyRun_File(file_1, "my_func.py",Py_file_input,main_dict, main_dict);
PyObject* expression = PyDict_GetItemString(main_dict,"find_sum");
printf("C: calling Python function...\n");
PyObject_CallFunction(expression,"ii",a,b);
//Clean up
fclose(file_1);
Py_Finalize();
}
Lastly, the Python script my_func.py:
def find_sum(a, b):
print a+b
When I run "python test.py", I get a segmentation fault at the second line of the C function:
PyObject* main_module = PyImport_AddModule("__main__");
Why is this happening? If I slightly rewrite the C routine so it is main, and run that program directly, I get the desired result. The problem seems to be related to having a Python interpreter calling a routine that initializes a Python interpreter.
So I have a Python program that's finding .txt file directories and then passing those directories as a list(I believe) to my C++ program. The problem I am having is that I am not sure how to pass the list to C++ properly. I have used :
subprocess.call(["path for C++ executable"] + file_list)
where file_list is the [] of txt file directories.
My arguments that my C++ code accepts are:
int main (int argc, string argv[])
Is this correct or should I be using a vector? When I do use this as my argument and try to print out the list I get the directory of my executable, the list, and then smiley faces, symbols, and then the program crashes.
Any suggestions? My main point that I am trying to find out is the proper syntax of utilizing subprocess.call. Any help would be appreciated! thanks!
Another option is to use cython, (not a direct answer). Here is a simple complete example:
Suppose you have the following files:
cython_file.cpp
python_file.py
setup.py
sum_my_vector.cpp
sum_my_vector.h
setup.py
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
ext_modules = [Extension(
name="cython_file",
sources=["cython_file.pyx", "sum_my_vector.cpp"],
extra_compile_args=["-std=c++11"],
language="c++",
)]
setup(
name = 'cython_file',
cmdclass = {'build_ext': build_ext},
ext_modules = ext_modules,
)
cython_file.pyx
from libcpp.vector cimport vector
cdef extern from "sum_my_vector.h":
int sum_my_vector(vector[int] my_vector)
def sum_my_vector_cpp(my_list):
cdef vector[int] my_vector = my_list
return sum_my_vector(my_vector)
sum_my_vector.cpp
#include <iostream>
#include <vector>
#include "sum_my_vector.h"
using namespace::std;
int sum_my_vector(vector<int> my_vector)
{
int my_sum = 0;
for (auto iv = my_vector.begin(); iv != my_vector.end(); iv++)
my_sum += *iv;
return my_sum;
}
sum_my_vector.h
#ifndef SUM_MY_VECTOR
#define SUM_MY_VECTOR
using namespace::std;
int sum_my_vector(vector<int> my_vector);
#endif
python_file.py
from cython_file import sum_my_vector_cpp
print sum_my_vector_cpp([1,2,3,5])
Now run
python setup.py build_ext --inplace
and the you can run the python file
python python_file.py
11
"Passing a list through Python to C++"
An alternative approach would be to use Boost.Python, this may not answer your question directly, but still its worth pointing out another solution.
#include <boost/python.hpp>
#include <vector>
#include <string>
void get_dir_list( boost::python::list dir_list )
{
for (int i = 0; i < len(dir_list); ++i)
{
std::string x = boost::python::extract<std::string>(dir_list[i]);
// perform stuffs
std::cout << "This is " << x << std::endl ;
}
}
BOOST_PYTHON_MODULE(get_dir_list)
{
def("get_dir_list", get_dir_list);
}
Compiled Using :
g++ main.cpp -shared -fPIC -o get_dir_list.so -I/usr/include/python2.7 -lboost_python
Usage :
import get_dir_list
import os
get_dir_list.get_dir_list(os.listdir('.'))
Live Demo Here
I'll post this alternative solution since it would also work for other long lists of strings that needed to be passed.
In your Python script create a text file (I'll call it "masterFile") and write the file paths to the masterFile. You could give each file path a separate line. Then pass the masterFile's file path to your C++ program. This way you don't have to worry about the length of your command line arguments. Let your C++ program open and read the file for processing.
You can use something like os.remove() to get rid of the masterFile in your Python script once the C++ program has finished.
Also, you mentioned in the comments that you need to do different tasks dependent on different file paths: A suggestion would be to add a char at the beginning of each line in the masterFile to signal what needs to be done for the particular file. Example:
a Random/path/aFile.txt # a could mean do task 1
b Random2/path2/differentFile.c # b could mean do task 2
You pass a list to subprocess.call. subprocess.call converts this to what is needed for the system (which may vary, but certainly isn't a Python list). The system then arranges for this to be copied somewhere in the new process, and sets up the standard arguments to main, which are int, char**. In your C++ program, you must define main as int main( int argc, char** argv ); nothing else will work. (At least... a system could support int main( std::string const& ) or some such as an extension. But I've never heard of one that did.)