The simpler C++ stuff is now well supported in Cython. Esoteric features will always cause troubles, but just using the std library is easy. Have a look at sage/tests/stl_vector.pyx for an example.
On Friday, September 27, 2013 5:00:07 PM UTC+1, mmarco wrote: > > I thought that C was easyer to interface from cython than C++ > > Anyways, the solution of passing the length of the array and then copying > the values one by one doesn't sound bad to me. > > El jueves, 26 de septiembre de 2013 15:28:37 UTC+2, Volker Braun escribió: >> >> Numpy only does machine datatypes and python objects. You can do a numpy >> array of python wrappers of mpfr reals but that would not be a good >> solution here. >> >> If the library is under your own control, I would recommend to use C++ >> instead of C and then design the interface around std::vector<double>. This >> is easier than C arrays, and more easily wrapped in Cython as well. >> >> >> On Thursday, September 26, 2013 2:14:29 PM UTC+1, Dima Pasechnik wrote: >>> >>> On 2013-09-25, Volker Braun <vbrau...@gmail.com> wrote: >>> > A pointer to a dynamically malloc'ed array doesn't know how long the >>> array >>> > is. Your C library function must returns its size, too. You can then >>> read >>> > it out one-by-one but you can't call list(c_array) since the latter >>> doesn't >>> > even know how long it is. >>> >>> I read somewhere that it is convenient to use numpy arrays in such >>> a situation (they are stored intrenally as C arrays, and there are extra >>> Python hooks kept by numpy). >>> Not sure I can reproduce details here. >>> >>> > >>> > >>> > >>> > On Wednesday, September 25, 2013 5:02:55 PM UTC+1, mmarco wrote: >>> >> >>> >> I see, thanks. >>> >> >>> >> So, if i understand it correctly, i import my_c_function and then, to >>> call >>> >> it, i create the memory space for the array, copy the data into it >>> and pass >>> >> the array to the function. >>> >> >>> >> I guess the result will be another c array that i can access from >>> python >>> >> in a transparent way, right? >>> >> >>> >> I mean, if i write: >>> >> >>> >> res=my_c_function(c_values) >>> >> >>> >> Then i can just use >>> >> >>> >> list(res) >>> >> >>> >> to get a list of floats? >>> >> >>> >> >>> >> El miércoles, 25 de septiembre de 2013 13:22:51 UTC+2, Volker Braun >>> >> escribió: >>> >>> >>> >>> Definitely use Cython. >>> >>> >>> >>> For array of doubles, say, you just need a sage/libs/my_library.pyx >>> with >>> >>> >>> >>> include "stdsage.pxi" >>> >>> >>> >>> cdef extern from "my_library.h" >>> >>> my_c_function(double*) >>> >>> >>> >>> def my_python_function(values): >>> >>> cdef double * c_values = <double*> >>> >>> sage_malloc(sizeof(double)*len(values)) >>> >>> for i,v in enumerate(values): >>> >>> c_values[i] = values[i] >>> >>> my_c_function(c_values) >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> On Wednesday, September 25, 2013 10:08:24 AM UTC+1, mmarco wrote: >>> >>>> >>> >>>> We are working on a c library to do homotoy continuation of >>> polynomial >>> >>>> roots using interval arithmetic. Our idea is to make a spkg with >>> it, and >>> >>>> write some functions in the sage library that would use it (in >>> particular, >>> >>>> to compute the fundamental group of the complement of an algebraic >>> curve). >>> >>>> so i have a question: >>> >>>> >>> >>>> how should we pass the data to the library, and retrieve it back? >>> Both >>> >>>> the input and output can be seen as an array of mpfr reals (or, >>> depending >>> >>>> on the version, floats or doubles). The length of the arrays is not >>> known a >>> >>>> priori. >>> >>>> >>> >>>> Which should be the best way to go? Write our interface in cython? >>> or >>> >>>> use ctypes? And in any case, is there some easy tutorial that we >>> could >>> >>>> follow? >>> >>>> >>> >>>> Thanks in advance. >>> >>>> >>> >>> >>> > >>> >>> -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/groups/opt_out.
