At Tuesday 26/9/2006 16:00, [EMAIL PROTECTED] wrote:
> >Q: The C idea of (pv != NULL) is said most directly in Python ctypes
> >how?
>
> Perhaps reading the ctypes tutorial? (both in the 2.5 docs and in
> <http://starship.python.net/crew/theller/ctypes/tutorial.html>)
Actually, no. I see three answers or zero, depending on how you like
to count.
Yes that flat edition helps makes this clear, thank you - there I can
more easily grab an ordered list of all matches of text than in the
more prominent shadow:
http://docs.python.org/dev/lib/module-ctypes.html
I see direct discussion only of how to construct null pointers, no
discussion of how to test for them. Specifically:
The hint { bool(null_ptr) == False } could be read to mean try ==
False, in the "Pointers" text.
It says:
NULL pointers have a False boolean value:
>>> null_ptr = POINTER(c_int)()
>>> print bool(null_ptr)
False
That means that NULL pointers are considered False in a boolean
expression (and you could assume that non-NULL pointers are True, as
any other object in general), so you can test a NULL pointer with a
simple "if ptr: whatever"
--- cut ---
from ctypes import *
null_ptr = POINTER(c_int)()
x=c_int(1234)
other_ptr = pointer(x)
if null_ptr: print "null_ptr is not NULL"
else: print "null_ptr is NULL"
if other_ptr: print "other_ptr is not NULL"
else: print "other_ptr is NULL"
--- cut ---
It's really the same as bool([])==False, bool(any_non_empty_list)==True:
L = [1,2,3]
while L:
print L.pop()
You don't say:
while bool(L)==True:
(do you?)
Gabriel Genellina
Softlab SRL
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