How to find out why import failed using PyImportModule?

Question

I have this code in a C application that embeds Python (2.7.1):

{ PyObject *user_dict; PyObject *user_func; PyObject *result; PyObject *header_tuple; PyObject *original_recipients; PyObject *working_recipients; if (!Py_IsInitialized()) { Py_Initialize(); } if (!expy_exim_dict) { PyObject *module = Py_InitModule(expy_exim_module, expy_exim_methods); /* Borrowed reference */ Py_INCREF(module); /* convert to New reference */ expy_exim_dict = PyModule_GetDict(module); /* Borrowed reference */ Py_INCREF(expy_exim_dict); /* convert to New reference */ } if (!expy_user_module) { if (expy_path_add) { PyObject *sys_module; PyObject *sys_dict; PyObject *sys_path; PyObject *add_value; sys_module = PyImport_ImportModule("sys"); /* New Reference */ if (!sys_module) { PyErr_Clear(); *return_text = "Internal error, can't import Python sys module"; log_write(0, LOG_REJECT, "Couldn't import Python 'sys' module"); return PYTHON_FAILURE_RETURN; } sys_dict = PyModule_GetDict(sys_module); /* Borrowed Reference, never fails */ sys_path = PyMapping_GetItemString(sys_dict, "path"); /* New reference */ if (!sys_path || (!PyList_Check(sys_path))) { PyErr_Clear(); /* in case sys_path was NULL, harmless otherwise */ *return_text = "Internal error, sys.path doesn't exist or isn't a list"; log_write(0, LOG_REJECT, "expy: Python sys.path doesn't exist or isn't a list"); return PYTHON_FAILURE_RETURN; } add_value = PyString_FromString(expy_path_add); /* New reference */ if (!add_value) { PyErr_Clear(); log_write(0, LOG_PANIC, "expy: Failed to create Python string from [%s]", expy_path_add); return PYTHON_FAILURE_RETURN; } if (PyList_Append(sys_path, add_value)) { PyErr_Clear(); log_write(0, LOG_PANIC, "expy: Failed to append [%s] to Python sys.path", expy_path_add); } Py_DECREF(add_value); Py_DECREF(sys_path); Py_DECREF(sys_module); } expy_user_module = PyImport_ImportModule(expy_scan_module); /* New Reference */ if (!expy_user_module) { PyErr_Clear(); /* Handle error */ } } 

When PyImport_ImportModule fails, it returns NULL. How can I find out why he could not import? (for example, when importing module work, detection is outside the attachment).

(The code is part of py-exim-localscan , and I want to add additional information about crashes in rare cases when they occur).

Answer 1

You do this by looking at the exception that has been raised. You are currently PyErr_Clear() exception (which is what PyErr_Clear() does). Do not do this and print a trace or check the exception object instead. See http://docs.python.org/c-api/exceptions.html for information on how to do this with C code, but generally, the best idea is to simply throw an exception.