Py_ParseTuple Problem

[youngdubliner]

Hi All ,

Bit of a problem with Py_Parse or Py_ParseTuple ?

I have a python script that reads a sector of flash in an embedded device.
it returns the value of each byte within the sector as a tuple.

i.e. [255,255,255,255,255,255,255, .......etc etc for the whole sector !

We are using this script to read whats currently in any sector.
No problems there.

Now I need to call our script from C.

I want to copy each of the bytes within the sector into an C unsigned char *array

Is there any way to do this using Py_ParseTuple or Py_Parse ???

something like this for instance ??? ......

Py_ParseTuple[pres,"??",&my_c_array]

so now my_c_array[0] = 255 ,my_c_array[1] = 255 ,my_c_array[2] = 255 , etc etc


Thanks for the help !

 

[Rick L. Ratzel]

I'm assuming you mean PyArg_Parse and PyArg_ParseTuple? I couldn't find
any docs on Py_Parse or Py_ParseTuple...

Anyway, maybe something like this might work for you (portions taken
from example in http://elmer.sourceforge.net/PyCon04/elmer_pycon04.html):

....
PyObject* evalModule;
PyObject* evalDict;
PyObject* evalVal;
PyObject* tupleItem;
unsigned char* my_c_array;
int i;
int tupleSize;

PyRun_SimpleString( "result = pyFuncWhichReadsDevice()" )

evalModule = PyImport_AddModule( (char*)"__main__" );
evalDict = PyModule_GetDict( evalModule );
evalVal = PyDict_GetItemString( evalDict, "result" );

if( evalVal == NULL ) {
PyErr_Print();
exit( 1 );

} else {
if( !PyTuple_Check( evalVal ) ) {
printf( "Error: pyFuncWhichReadsDevice() did not return a tuple" );
exit( 1 );
}

my_c_array = (unsigned char*) malloc( sizeof( unsigned char ) *
PyTuple_Size( evalVal ) );

tupleSize = PyTuple_Size( evalVal );

for( i=0; i < tupleSize; i++ ) {
tupleItem = PyTuple_GetItem( evalVal, i );

if( !PyInt_Check( tupleItem ) ) {
printf( "Error: pyFuncWhichReadsDevice() returned tuple with
non-int value" );
exit( 1 );
}
my_c_array = (unsigned char) PyInt_AsLong( tupleItem );
}
}
....

I have no idea if this will work for you since I haven't even tried
to compile it...consider it pseudo-code.

-Rick.

 

[Terry Reedy]

Hi All ,

Bit of a problem with Py_Parse or Py_ParseTuple ?

I have a python script that reads a sector of flash in an embedded device.
it returns the value of each byte within the sector as a tuple.

i.e. [255,255,255,255,255,255,255, .......etc etc for the whole sector !

As written, above is a list instead of a tuple.

We are using this script to read whats currently in any sector.
No problems there.

Now I need to call our script from C.

I want to copy each of the bytes within the sector into an C unsigned

char *array

Without knowing the C API, I would try to generate byte string from within
Python. Three possibilities:

1. turn list into string - secstring = ''.join(map(chr, seclist)). Then
use C API to get the cstring from string object.

2. turn list/tuple into array (of unsigned chars) or built that directly
instead of list or tuple. See array module. I presume you can get at the
buffer itself from C API.

3. look into ctypes module.

Is there any way to do this using Py_ParseTuple or Py_Parse ???

If you mean PyArg.... stuff, I believe these are meant for parsing
argu;ments passed as heterogeneous Python tuple, which is quite different
from what you want to do.

Terry J. Reedy

 

[youngdubliner]

Thanks Rick ,

Thats excellent I tried your code , changed it a little and it works
really well.

I didn't even know that PyTuple_Size() existed , handy little function that.

Thanks again !

Keith.