__init__.py descends dirtree for python, but not from c++; causes "import matplotlib" error.

Question

Why or how does the file __init__.py cause the python interpreter to search subdirectories for a module -- and why does the interpreter not honor this convention when invoked from C++?

Here's what I know:

Using strace on my program, I can see that the same python2.5 interpreter is being executed for both the interactive case and the C++ invocation.

In both cases, the PYTHONPATH directs the search for the imported module in question (matplotlib). This appears as a series of open() calls, starting from the current working directory and extending to the PYTHONPATH (here, /opt/epd/lib/python2.5/site-packages), and lastly into the subdirectories, in the working case.

The full disclosure is that I am using the "Enthought" distribution and had to place the __init__.py file in the site-packages directory and put the site-packages directory in the PYTHONPATH to create the working case.

The code is below. It seems that I may need to make a call to configure the python interpreter to look for __init__ and/or recurse, in order to find the requested packages. IF SO, HOW??

PyObject* main_module, * global_dict, * expression, *args, *spec;

Py_Initialize ();

char* script = "abc.py";
PySys_SetArgv(1, &script);

//Open the file containing the python modules we want to run
FILE* file_1 = fopen("abc.py", "r");
if (file_1 == 0) fprintf(stdout, "ERROR: File not opened");

//Loads the python file into the interpreter
PyRun_SimpleFile(file_1, "abc.py");

//Creates a python object that contains references to the functions and classes in abc.py 
main_module = PyImport_AddModule("__main__");
global_dict = PyModule_GetDict(main_module);

expression = PyDict_GetItemString(global_dict, "view_gui");
spec       = PyObject_CallObject(expression, NULL);

PyObject_CallMethod(spec, "shutdown", NULL);
Py_Finalize();

return NULL;

When the python script is invoked from C++, the search seems to stop when the file /opt/epd/lib/python2.5/site-packages/matplotlib (or it's variant, matplotlib.so, etc) are not found.

Note that I can augment the PYTHONPATH to include the exact location of matplotlib (and other needed packages) to get farther; however, I cannot seem to include a path to import matplotlib.cbook.

Answer 1

Looking at (a different version # of) python, I see that import.c has the find_init_module(), which is a part of the find_module(). Not evident why find_init_module() is not executed or fails.