I have a Cython extension class that wraps the N_Vector type [1] from the
Sundials solver suite for differential equations. (Thanks to Dag Sverre
Seljebotn for guidance [2].) However, I have problems using the class outside
of the module where it was defined (cynvector.pyx).
The following couple of trivial operations work when included at the end of
cynvector.pyx:
cdef CythonNVector v = CythonNVector(2) # allocates empty N_Vector of length 2
cdef N_Vector p = v.nvector # alias to an attribute of the CythonNVector
(I've learned that both v and p need to have their type specified by
"cdef ...", otherwise they default to generic Python objects and the "nvector"
attribute isn't recognized.)
However, the same statements fail if I move them to another file, say
test_cynvector.pyx:
from sundials cimport * # sundials.pxd contains type declaration for N_Vector
from cynvector import *
cdef CythonNVector v = CythonNVector(2) # allocates empty N_Vector of length 2
cdef N_Vector p = v.nvector # alias to an attribute of the CythonNVector
fails with:
cdef CythonNVector v = CythonNVector(2)
^
'CythonNVector' is not a type identifier
Why isn't type CythonNVector recognized outside of cynvector.pyx? A similar
error results if I try "from cynvector cimport CythonNVector"; then I get "Name
'CythonNVector' not declared in module 'cynvector'".
Thanks in advance for any help.
[1] https://computation.llnl.gov/casc/sundials/documentation/cv_guide/node7.html
[2] http://article.gmane.org/gmane.comp.python.cython.devel/6556
Here is the essence of cynvector.pyx, based on [2]:
== cynvector.pyx ==
cimport numpy as np
from sundials cimport * # sundials.pxd declares N_Vector and friends
cdef extern from "pyarray_set_base.h":
void PyArray_Set_BASE(np.ndarray arr, object obj)
cdef extern from "numpy/arrayobject.h":
void import_array()
object PyArray_SimpleNewFromData(int nd, np.npy_intp* dims,
int typenum, void* data)
import_array()
cdef class CythonNVector:
cdef N_Vector nvector
def __init__(self, length):
self.nvector = N_VNew_Serial(length)
def __dealloc__(self):
N_VDestroy_Serial(self.nvector)
cpdef toarray(self):
cdef np.npy_intp* shape = <np.npy_intp *>(
&(<N_VectorContent_Serial>(self.nvector).content).length)
assert sizeof(realtype) == sizeof(double)
cdef np.ndarray result = PyArray_SimpleNewFromData(1, shape,
np.NPY_DOUBLE,
<void*>((<N_VectorContent_Serial>(self.nvector).content).data))
PyArray_Set_BASE(result, self)
return result
# Testing: These statements do work at the end of cynvector.pyx.
cdef CythonNVector v = CythonNVector(2)
cdef N_Vector p = v.nvector
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