[Python] If I have a cdef or cpdef function which uses yield, what type should it be?

I have a generator function (a function which uses the yield statement).

Specifically, it is a part of a Cythonized thing I'm working on to have Python play Sudoku. (Yes, that is trivial, but it's what I'm working on right now and it is relevant to other things.)

That's part 1 of establishing context. Part 2 is that the Sudoku grid is stored as a list of lists of Cells (extension type because I can do so, for this it might as well be a smart integer that can work out what it could, and even should, be based on the other instances that have been fed to it - anyway).

Here's the portion of the code in question:

cpdef box_gen(self):
cdef:
unsigned char y1, x, y2
list box
for y1 in range(0,9,3):
for x in range(0,9,3):
box = []
for y2 in range(y1,y1+3):
box.extend(self.grid[y2][x:x+3])
yield [cell.c for cell in box]
cpdef row_gen(self):
cdef:
list row
for row in self.grid:
yield [x.c for x in row]
cpdef col_gen(self):
cdef:
char i
for i in range(9):
yield [row.c for row in self.grid]


Oh, also, the numeric value of a Cell (or 0 if they has yet to be determined or assigned) is stored in the attribute 'c'.

So: What should I type these functions as? Is there a type I need to cimport from cpython? Is there something I need to grap using a cdef extern block?

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