Embedded python code in c++ - error when importing python libraries

Question

I am trying to use Python 3.5 interpreter embedded in a C++ program to receive an image from C++, and use it as an input for my trained tensorflow model. First, I convert my image to numpy array and then send it to python. This is my simplified code which works fine (codes adopted from here):

Python code:

def multiply_fun(M):
    V = M*2
    print(V)

My C++ code that calls the function above:

#include <Python.h>
#include <abstract.h>
#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
#include <ndarrayobject.h>
#include <vector>


int main()
{
    Py_InitializeEx(1);

    PyObject* sysPath = PySys_GetObject((char*)"path");
    PyObject* curDir = PyUnicode_FromString(".");
    PyList_Append(sysPath, curDir);
    Py_DECREF(curDir);

    PyObject* python_code = PyImport_ImportModule("python_code");
    PyObject* multiply_fun = PyObject_GetAttrString(python_code, "multiply_fun");
    Py_XDECREF(python_code);

    import_array1(-1);
    npy_intp dim[] = { 5, 5 };
    std::vector<double> buffer(5*5, 1);

    PyObject* array_2d = PyArray_SimpleNewFromData(2, dim, NPY_DOUBLE, &buffer[0]);
    PyObject* return_value1 = PyObject_CallFunction(multiply_fun, "O", array_2d);

    Py_XDECREF(return_value1);
    Py_XDECREF(array_2d);
    Py_XDECREF(multiply_fun);

    Py_Finalize();
    return 0;
}

However, when I want to use most of the python libraries, I get an error. For example, for this python code:

def multiply_fun(M):
    from skimage.io import imsave
    imsave('test.png', M)

I got this error:

Exception ignored in: <module 'threading' from 'C:\\Users\\Matin\\Anaconda3\\Lib\\threading.py'>
Traceback (most recent call last):
  File "C:\Users\Matin\Anaconda3\Lib\threading.py", line 1283, in _shutdown
    assert tlock.locked()
SystemError: <built-in method locked of _thread.lock object at 0x0000000002AF4418> returned a result with an error set

By the way, This related discussion couldn't help me.

Thanks for your help.

EDIT 1: By moving from skimage.io import imsave to outside of the python function (as @moooeeeep suggested in comments) I get Null in this line:

PyObject* python_code = PyImport_ImportModule("python_code");

Matin H · Accepted Answer · 2017-09-14 06:57:52Z

1

It seems the problem is that PyImport_ImportModule cannot load submodules of some packages when using from package.submodule import function. It has been explained in Python/C API Reference Manual:

When the name argument contains a dot (when it specifies a submodule of a package), the fromlist argument is set to the list ['*'] so that the return value is the named module rather than the top-level package containing it as would otherwise be the case. (Unfortunately, this has an additional side effect when name in fact specifies a subpackage instead of a submodule: the submodules specified in the package’s all variable are loaded.) Return a new reference to the imported module, or NULL with an exception set on failure. A failing import of a module doesn’t leave the module in sys.modules.

This function always uses absolute imports.

edited Sep 14, 2017 at 6:57

answered Sep 13, 2017 at 6:36

Matin H

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1 Comment

Matin H Over a year ago

I got new error when importing tensorflow. this is my new problem.

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