Sometimes one ends up with implementing really small access routines,
just to do a lookup for something. In cython you might even want to do
that with some "cdef" methods. For general accessibility, you might
consider slapping a "cpdef" on rather than a "cdef". That may come at
a serious price, because "cpdef" methods also check if they have been
overridden on the instance or via subclassing if they get called via
their cdef interface:
with the following code we get:
cython("""
cdef class A(object):
cpdef int a(self):
return 0
cdef int b(self):
return 0
cpdef int test_a(self, long N):
cdef long i
for i in xrange(N):
self.a()
return 0
cpdef int test_b(self, long N):
cdef long i
for i in xrange(N):
self.b()
return 0
""")
t=A()
timeit('t.test_a(10000000)')
timeit('t.test_b(10000000)')
class B(A):
pass
s=B()
timeit('s.test_a(10000000)')
timeit('s.test_b(10000000)')
25 loops, best of 3: 21.2 ms per loop
25 loops, best of 3: 15.9 ms per loop
5 loops, best of 3: 507 ms per loop
25 loops, best of 3: 15.9 ms per loop
As you can see for A it's not so bad, because there's no instance
dict. However, for the subclassed s there is an instance dict. Now the
cpdef method s.a (even inside the cython!) checks every time if it has
been overridden with a full attribute lookup.
Timings improve with attribute caching turned on (of course only for
s.test_a, because the other tests hardly do any attribute lookup)
25 loops, best of 3: 21.2 ms per loop
25 loops, best of 3: 15.9 ms per loop
5 loops, best of 3: 303 ms per loop
25 loops, best of 3: 16 ms per loop
but the penalty is still significant if your routine does very little
by itself. This was certainly unexpected for me. I was expecting that,
as far as cdef is concerned, the p in cpdef would have no effect.
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