Python Programming Language :: Embedding Python in C


	Embedding Python in C Hello, first of all, I am a programming newbie, especially in python... Onwards to the problem, I have been having difficulty embedding a python module into my C/C++ program. (just a test program before moving on into the real thing). I have been making test runs using the codes from http://docs.python.org/ext/pure-embedding.html as a basic, but modifiying it now as a function inside my C/C++ code. Problem started when I started passing an array as an argument. The module also need an array as an argument, but somehow I can't make them to go pass the "input-error checking" of the module. The code for argument building and calling are as follows: void CallSnake(char ModName[], char FuncName[], double result[]) { ... /Some operations to import modname, and preping FuncName, all is ok/ ... /Processing the result array and calling the function, problem time/ pArgs = PyTuple_New(MAX_ELEMENT); pArg = PyList_New(1); for (i = 0; i < MAX_ELEMENT; ++i) { pValue = Py_BuildValue("d", result[i]); PyTuple_SetItem(pArgs, i, pValue); if (!(pArgs).ob_refcnt) { Py_DECREF(pArgs); Py_DECREF(pModule); fprintf(stderr, "Cannot convert argument\n"); return; } } PyList_SetItem(pArg, 0, pArgs); pValue = PyObject_CallFunctionObjArgs(pFunc,pArg,NULL); /Some more checking and DECREFing occurs here/ } Error I have been getting is: Traceback if x.ndim != 1; /x is the input array, checking if it's a 1D/ AttributeError: 'list' object has no attribute 'ndim' I have been trying many call variations, but alas, I think the problem lies in the list building process. I have no problems calling a non- arrayed (albeit,still single) argument. Thanks in advance... En Mon, 04 Jun 2007 11:58:38 -0300, <mistab@gmail.com> escribi: - Hide quoted text - > Onwards to the problem, I have been having difficulty embedding a > python module into my C/C++ program. (just a test program before > moving on into the real thing). I have been making test runs using the > codes from http://docs.python.org/ext/pure-embedding.html as a basic, > but modifiying it now as a function inside my C/C++ code. > Problem started when I started passing an array as an argument. The > module also need an array as an argument, but somehow I can't make > them to go pass the "input-error checking" of the module. > The code for argument building and calling are as follows: > void CallSnake(char ModName[], char FuncName[], double result[]) > { > ... > /Some operations to import modname, and preping FuncName, all is > ok/ > ... > /Processing the result array and calling the function, problem > time/ > pArgs = PyTuple_New(MAX_ELEMENT); Should check for a NULL return value. > pArg = PyList_New(1); Same here. > for (i = 0; i < MAX_ELEMENT; ++i) > { > pValue = Py_BuildValue("d", result[i]); I'd use PyFloat_FromDouble here. > PyTuple_SetItem(pArgs, i, pValue); > if (!(pArgs).ob_refcnt) What do you expect from this? pArgs is a newly created tuple - unless you DECREF it explicitely, ob_refcnt should never be 0. (Also, the -> operator exists for exactly this usage). > PyList_SetItem(pArg, 0, pArgs); > pValue = PyObject_CallFunctionObjArgs(pFunc,pArg,NULL); You didn't show us how you got pFunc here. Just to make it clear, you are calling pFunc with a single argument, which is a list that contains a single element, which is a tuple containing exactly MAX_ELEMENT float objects. > Traceback > if x.ndim != 1; /x is the input array, checking if it's a 1D/ > AttributeError: 'list' object has no attribute 'ndim' Python lists don't have a ndim attribute. Perhaps you want some kind of Numeric array? (ndarray?) > I have been trying many call variations, but alas, I think the problem > lies in the list building process. I have no problems calling a non- > arrayed (albeit,still single) argument. Yes, it appears that you are building a plain list but your code is expecting another kind of object. I'm unfamiliar with Numeric arrays, if that is what you need; perhaps someone else can help, or ask again in a Numeric-specific list. -- Gabriel Genellina On 5 Jun., 01:32, "Gabriel Genellina" <gagsl-@yahoo.com.ar> wrote: - Hide quoted text - > En Mon, 04 Jun 2007 11:58:38 -0300, <mistab@gmail.com> escribi: > > Onwards to the problem, I have been having difficulty embedding a > > python module into my C/C++ program. (just a test program before > > moving on into the real thing). I have been making test runs using the > > codes fromhttp://docs.python.org/ext/pure-embedding.htmlas a basic, > > but modifiying it now as a function inside my C/C++ code. > > Problem started when I started passing an array as an argument. The > > module also need an array as an argument, but somehow I can't make > > them to go pass the "input-error checking" of the module. > > The code for argument building and calling are as follows: > > void CallSnake(char ModName[], char FuncName[], double result[]) > > { > > ... > > /Some operations to import modname, and preping FuncName, all is > > ok/ > > ... > > /Processing the result array and calling the function, problem > > time/ > > pArgs = PyTuple_New(MAX_ELEMENT); > Should check for a NULL return value. > > pArg = PyList_New(1); > Same here. > > for (i = 0; i < MAX_ELEMENT; ++i) > > { > > pValue = Py_BuildValue("d", result[i]); > I'd use PyFloat_FromDouble here. > > PyTuple_SetItem(pArgs, i, pValue); > > if (!(pArgs).ob_refcnt) > What do you expect from this? pArgs is a newly created tuple - unless you > DECREF it explicitely, ob_refcnt should never be 0. (Also, the -> operator > exists for exactly this usage). > > PyList_SetItem(pArg, 0, pArgs); > > pValue = PyObject_CallFunctionObjArgs(pFunc,pArg,NULL); > You didn't show us how you got pFunc here. Just to make it clear, you are > calling pFunc with a single argument, which is a list that contains a > single element, which is a tuple containing exactly MAX_ELEMENT float > objects. > > Traceback > > if x.ndim != 1; /x is the input array, checking if it's a 1D/ > > AttributeError: 'list' object has no attribute 'ndim' > Python lists don't have a ndim attribute. Perhaps you want some kind of > Numeric array? (ndarray?) > > I have been trying many call variations, but alas, I think the problem > > lies in the list building process. I have no problems calling a non- > > arrayed (albeit,still single) argument. > Yes, it appears that you are building a plain list but your code is > expecting another kind of object. I'm unfamiliar with Numeric arrays, if > that is what you need; perhaps someone else can help, or ask again in a > Numeric-specific list. > -- > Gabriel Genellina- Zitierten Text ausblenden - > - Zitierten Text anzeigen - yeah, i was looking at am array full of numbers. import numpy,scipy, maybe pylab too while i was testing out the function over at a python shell, make a linspace, sin it, and then call the function (which also is from the scipy cookbook). Is numeric arrays (or ndarray) unlike normal listing then? Since I started off programming in C, I am having a bit of a confusion identifiying the different type of arrays, listing and tuples and such... (since it's just "build an array of type so and so, and pass it over" ^^;;) the reason i didn't show pFunc is that because it is the result of operations done to FuncName (ModName = module to be imported, FuncName = function to be called), therefore i feel it would be a bit waste of time/space to put in the pFunc function, since I didn't change the operations concerning pFunc other than changing argv[1] to FuncName from the link i gave (and not the core of my problem). so yeah, maybe I am building and passing the array/calling the function the wrong way... will have to take a look at numpy/numerical specific C API and stuff now thanks for your time and the help now then... where's the edit button...? oh well, double-posting. Problem solved, thanks for pointing out that I am needing a numeric array built instead of building a normal list/ tuple. For those who are curious, steps to solving: ... #include "libnumarray.h" /from numpy/ ... ... ... void CallSnake(...) { ... ... Py_Initialize(); import_libnumarray(); /badgered me to call this one... where i don't know/ ... ... pArray = NA_InputArray(pArgs, tFloat32, NUM_C_ARRAY); /instead of making a pArg and calling PyList_SetItem(pArg, 0, pArgs); / /Check for NULL on pArray/ pValue = PyObject_CallFunctionObjArgs(pFunc,pArray,NULL); /error checking, cleaning up, Finalizing etc etc/ - Hide quoted text - } This seems like a pretty good resource, although I didn't read it all yet: http://www.ibm.com/developerworks/edu/l-dw-linux-pythonscript-i.html En Tue, 05 Jun 2007 03:41:19 -0300, <mistab@gmail.com> escribi: > On 5 Jun., 01:32, "Gabriel Genellina" <gagsl-@yahoo.com.ar> wrote: >> Yes, it appears that you are building a plain list but your code is >> expecting another kind of object. I'm unfamiliar with Numeric arrays, if >> that is what you need; perhaps someone else can help, or ask again in a >> Numeric-specific list. > yeah, i was looking at am array full of numbers. import numpy,scipy, > maybe pylab too while i was testing out the function over at a python > shell, make a linspace, sin it, and then call the function (which also > is from the scipy cookbook). Is numeric arrays (or ndarray) unlike > normal listing then? Since I started off programming in C, I am having > a bit of a confusion identifiying the different type of arrays, > listing and tuples and such... (since it's just "build an array of > type so and so, and pass it over" ^^;;) I've seen that you have already solved your main problem, but anyway I'll try to reduce your confusion a little... Python lists and tuples are "generic" containers: both can contain any kind of object, and each item may be of a different type: (1, 2.0, 3+0j, "four", u"Fnf", file("six")) is a tuple containing 6 items, all of different types. Tuples are immutable, lists can be modified. There is a price for such flexibility: memory and time overhead. When you don't require flexibility, you don't have to pay the price; Python already provides simple array objects (a flat container where ALL items are of the same type) and Numeric&Co support more array types and different floating point numbers. Those arrays are not the same thing as lists/tuples - altough they share a very similar interfase. -- Gabriel Genellina On 6 Jun., 05:44, "Gabriel Genellina" <gagsl-@yahoo.com.ar> wrote: > Python lists and tuples are "generic" containers: both can contain any > kind of object, and each item may be of a different type: (1, 2.0, 3+0j, > "four", u"Fnf", file("six")) is a tuple containing 6 items, all of > different types. Tuples are immutable, lists can be modified. > There is a price for such flexibility: memory and time overhead. When you > don't require flexibility, you don't have to pay the price; Python already > provides simple array objects (a flat container where ALL items are of the > same type) and Numeric&Co support more array types and different floating > point numbers. > Those arrays are not the same thing as lists/tuples - altough they share a > very similar interfase. > -- > Gabriel Genellina Hmmmm, interesting to know that multi-type...errr... "thingys" can be packed into one tuple or list. I think my problem of not recognizing what array is what type will be solved in time hopefully*. "Joe Riopel" wrote: >This seems like a pretty good resource, although I didn't read it all yet: >http://www.ibm.com/developerworks/edu/l-dw-linux-pythonscript-i.html Thanks for the link. Every resource is useful, in one way or another.