Polymorphism with cython extesion types - cython

Question

I have a cython extension type that I want to make more general. One of the attributes of this extension type is a double and I want it to be a memoryview (double[::1]) when needed.
Here is a simple example :
import numpy as np
cimport numpy as np
cimport cython
cdef class Test:
cdef bint numeric
cdef double du
def __init__(self, bint numeric):
self.numeric = numeric
if self.numeric:
self.du = 1
else:
self.du = np.ones(10)
def disp(self)
print(self.du)
Test(True).disp() # returns 1
Test(False).disp() # gives of course an error
I tried to subclass Test changing du type to double[::1] and implementing a new __init__ but it seems that we can't override class attributes of extension types. Even if it worked, it wouldn't be satisfactory because I don't really want to have one extension type for each case.
The best would be that my extension type directly handle both cases (scalar du and memoryview du).
Is there a way to do this with Cython ?

Answer 1

Unfortunately, you cannot use fused_type as attributes type. You can have two options here:
You could try to use the memory adress of the variable you want to call, and cast it when needed (everything is explained here.) Unfortunately, I did not succeed at making it work with typed memory views.
Or you can use your defined attribute numeric to call the appropriate method:
import numpy as np
cimport numpy as np
cimport cython
cdef class Test:
cdef bint numeric
cdef double du_numeric
cdef double[:] du_mem_view
def __init__(self, bint numeric):
self.numeric = numeric
if self.numeric:
self.du_numeric = 1
else:
self.du_mem_view = np.ones(10)
def disp(self):
if self.numeric:
print(self.du_numeric)
else:
print(self.du_numeric_mem_view)
Test(True).disp() # returns 1
Test(False).disp() # Does not give an error anymore !