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Date: Tue, 12 Nov 2013 12:44:12 +0100
From: Dominik Weinhold <djweinhold@web.de>
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Subject: Python and Android: PyImport_ImportModule always returns NULL
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Hello all together,

I have  a python and android related issue. I hope that this is no 
problem because apart from stack overflow, where I also posted this 
question (but got no answer so far), I think a python mailing-list is 
the best place to post this question.

I am trying to use Python-Scripts in Android. So far a managed to get 
python as a shared library and linked it to my android project using 
Android.mk. I also created a file named wrapper.c which gets called from 
Java using jni and is used to call the python-script using the 
Python-C-Api. But when I try to open the script using 
PyImport_ImportModul, it always returns NULL.

First here is my Android.mk file which I put in the jni-folder of my 
Android project:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE := luajit
LOCAL_SRC_FILES := libluajit.so
include $(PREBUILT_SHARED_LIBRARY)

include $(CLEAR_VARS)
LOCAL_SHARED_LIBRARIES := luajit
LOCAL_SHARED_LIBRARIES += libcutils
LOCAL_LDLIBS := -llog
LOCAL_MODULE := wrapper
LOCAL_SRC_FILES := wrapper.c
LOCAL_EXPORT_C_INCLUDES := .
include $(BUILD_SHARED_LIBRARY)
This file does not cause any problems so far. wrapper.c is the c-file 
which is called from java using jni. This file uses the Python-C-Api to 
call a Python script. This is wrapper.c:

jstring
Java_com_example_pythonandroid_MainActivity_stringFromJNI(JNIEnv* env 
jobject thiz, jstring filename, jstring path) {
     PyObject *modul, *funk, *ret;
     char *erg;


     const char *filenameCString = (*env)->GetStringUTFChars(env, 
filename, 0);
     char *pathCString = (*env)->GetStringUTFChars(env, path, 0);
     __android_log_print(ANDROID_LOG_INFO, "CFilename", filenameCString);
     __android_log_print(ANDROID_LOG_INFO, "CPath", pathCString);
     Py_Initialize();
     PySys_SetPath(pathCString);

     modul = PyImport_ImportModule(filenameCString);
     if(modul!=NULL) {
         funk = PyObject_GetAttrString(modul, "helloPy");
         ret = PyObject_CallObject(funk, NULL);
         erg = PyString_AsString(ret);
         __android_log_print(ANDROID_LOG_INFO, "pyAnswer", erg);

         Py_DECREF(ret);
         Py_DECREF(funk);
         Py_DECREF(modul);

         Py_Finalize();
         return (*env)->NewStringUTF(env, erg);
     } else {
         return (*env)->NewStringUTF(env, "Error: Modul not found");
     }
}

Filename and Path (set on the java-site) in this case are:

/data/data/com.example.pythonandroid/files/test.py
/data/data/com.example.pythonandroid/files
The file test.py was placed in the res/raw folder of the Android Project.

To check if they refer to the correct file, I printed the file 
/data/data/com.example.pythonandroid/files/test.py in wrapper.c and got 
the content of my python script. So everything seems to be alright on 
this end.

 From the information I've read so far I understand that I have to set 
PySys_SetPath to the path where Python should look for modules. After 
that I can import them which PyImport_ImportModule. I also tried to set 
PySys_SetPath(".") even though it seems unrealistic that the actual path 
and the path of the script are the same. Anyway: it didn't work.

I hope I gave you all the information you need. Thanks in advance.

greetings
Dominik