En Wed, 11 Jun 2008 04:21:03 -0300, Gabriel Rossetti
<[EMAIL PROTECTED]> escribió:
Gabriel Genellina wrote:
En Tue, 10 Jun 2008 09:44:13 -0300, Gabriel Rossetti
<[EMAIL PROTECTED]> escribió:
I wanted to use the h2py.py script (Tools/scripts/h2py.py) and it
didn't like char litterals :
Skipping: PC_ERROR = ord()
where my *.h file contained :
#define PC_ERROR '0'
I searched the web and found a post with the same error :
http://mail.python.org/pipermail/python-list/2005-September/340608.html
but it got no replies, I tried the fix and it works. I have the
following questions:
1) Why did it not get any attention, is something wrong with it?
2) If nothing is wrong, did the fix not get applied because a bug
report wasn't filed?
Very probably - bug reports outside the tracker are likely to go
unnoticed or forgotten.
Ok, I'll file one then.
3) Isn't turning a char literal into the ordinal value not contrary to
what a C programmer had in mind when he/she defined it? I mean if you
define a char literal then in python you would have used a string
value :
#define PC_ERROR '0'
would become :
PC_ERROR = '0'
in python, and if you intended to use the char type for an 8 bit
numerical value you would have done :
#define PC_ERROR 0x30
where 0x30 is the '0' ascii hex value, so shouldn'it the line in the
diff (see the post) be :
body = p_char.sub("'\\1'", body)
instead of :
body = p_char.sub("ord('\\1')", body)
It's not so clear what's the intended usage - chars are also integers
in C. (I prefer the current behavior, but certainly it may be wrong in
several places).
Yes, true, but if you intend to use it as an integer, wouldn't you use a
numeric value instead of a character literal?
Not always. Using characters as ordinal numbers is very common in that
language. A small example:
#define FIRST 'A'
#define LAST 'Z'
#define index(letter) ((letter)-FIRST)
int accum[LAST-FIRST+1];
...
char x = some_word[0];
accum[index(x)]++;
accum is an array of 26 integers, element 0 corresponding to letter 'A'.
If one has to reproduce the exact same structure, in Python it would be:
FIRST = ord('A')
LAST = ord('Z')
def index(letter):
return ord(letter)-FIRST
accum = [0 for i in range(LAST-FIRST+1)]
x = some_word[0]
accum[index(x)] += 1
Of course, in other cases, character constants are intended to be used as
character data, so ord(...) is not the appropiate thing to do when
converting to Python. But I don't think my example above is very contrived
or uncommon - chars *are* integers from the C point of view, and some
people isn't worried too much about the distinction, specially those who
use C as their main or only language.
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
