On Fri, 20 Oct 2006 02:16:30 -0700, Joshua Kantor
<[EMAIL PROTECTED]> wrote:
> The example I send I had modified before sending it and
> apparently in that example the Py_INCREF I had isn't necessary,
> I've attached the original example I had where it is necessary.
> Consider foo vs foo_bar. foo works once but crashes if you run it again
> on
> the same tuple or try and do anything with that tuple foo_bar works fine
> repeatedly no crashes.
>
This is a very good sign that you're doing something right:
sage: time foo_bar(range(10^6))
CPU times: user 0.29 s, sys: 0.01 s, total: 0.29 s
Wall time: 0.30
499999500000L
sage: time sum(range(10^6))
CPU times: user 0.31 s, sys: 0.01 s, total: 0.31 s
Wall time: 0.32
499999500000L
I tried another function I just saw in the Python/C API, and I'm
able to *beat* the built-in sum function. Cool!
sage: time mysum(range(10^6))
CPU times: user 0.29 s, sys: 0.01 s, total: 0.29 s
Wall time: 0.30
499999500000L
sage: time sum(range(10^6))
CPU times: user 0.31 s, sys: 0.01 s, total: 0.32 s
Here's how mysum is defined in Pyrex. Note the trick of void
pointers to avoid Pyrex reference counting, etc:
cdef extern from "Python.h":
object PySequence_Fast(object,char *)
int PySequence_Size(object)
object PySequence_Fast_GET_ITEM(object, int)
void** PySequence_Fast_ITEMS(object o)
void Py_INCREF(object)
def mysum(x):
cdef object seq
cdef int len,i
cdef object item
cdef object total
total = 0
seq = PySequence_Fast(x,"Expected sequence")
len = PySequence_Size(x)
cdef void** X
X = PySequence_Fast_ITEMS(seq)
for i from 0 <=i<len:
item = <object>X[i]
total = total + item
return (total)
So, maybe this is the best way to iterate through a Python list.
William
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