Call a Python function from within a C program

问题

I have an application in C and at some point I need to solve a non-linear optimization problem. Unfortunately AFAIK there are very limited resources to do that in C (please let me know otherwise). However it is quite simple to do it in Python, e.g. scipy.optimize.minimize.

While I was trying to do that I encountered some of what it seems to be very frequent pitfalls, e.g. Python.h not found, module not loading, segmentation fault on function call, etc.

What is a quick and easy first-timer’s way to link the two programs?

回答1:

There are some things that you have to make sure are in place in order to make this work:

Make sure you have Python installed (you may need the python-dev package).
Locate your Python.h file, e.g. by locate Python.h. One of the occurrences should be in a sub(sub)folder in the include folder, e.g. the path should be something like ../include/python2.7/Python.h.
Insert #include “<path_to_Python.h>" in your C code in order to be able to use the Python API.
Use any tutorial to call your Python function. I used this one and it did the trick. However there were a couple of small points missing:
- Whenever you use any Py<Name> function, e.g. PyImport_Import(), always check the result to make sure there was no error, e.g.
```
// Load the module object
pModule = PyImport_Import(pName);

if (!pModule)
{
    PyErr_Print();
    printf("ERROR in pModule\n");
    exit(1);
}
```
- Immediately after initializing the Python interpreter, i.e. after Py_Initialize();, you have to append the current path to sys.path in order to be able to load your module (assuming it is located in your current directory):
```
PyObject *sys = PyImport_ImportModule("sys");
PyObject *path = PyObject_GetAttrString(sys, "path");
PyList_Append(path, PyString_FromString("."));
```
Keep in mind that when you give the name of your Python file, it has to be without the extension .py.
Lastly, you have to do the following during compiling/linking:
- Remember the ../include/python2.7/Python.h file you used before? Include the include folder in the list of the header files directories with the -I option in the gcc options during compilation, e.g. -I /System/Library/Frameworks/Python.framework/Versions/2.7/include.
- Also pass to the linker the folder with the required libraries. It should be inside the same folder where the include folder is located, e.g. -L /System/Library/Frameworks/Python.framework/Versions/2.7/lib, along with the -lpython2.7 option (of course adjusting it accordingly to your Python version).

Now you must be able to successfully compile and execute your C program that calls in it your Python program.

I hope this was helpful and good luck!

Sources:

How do you call Python code from C code?
http://www.linuxjournal.com/article/8497?page=0,1
http://www.codeproject.com/Articles/11805/Embedding-Python-in-C-C-Part-I
http://www.codeproject.com/Articles/11843/Embedding-Python-in-C-C-Part-II
Python C API doesn't load module
What sets up sys.path with Python, and when?
http://linux.die.net/man/1/gcc
PyObject segfault on function call
I have Python on my Ubuntu system, but gcc can't find Python.h
How do you call Python code from C code?

来源：https://stackoverflow.com/questions/25316485/call-a-python-function-from-within-a-c-program

标签

python

c++

python-c-api