gagsl-py2 at yahoo.com.ar
Thu Jun 12 11:29:41 CEST 2008
En Wed, 11 Jun 2008 04:21:03 -0300, Gabriel Rossetti
<gabriel.rossetti at arimaz.com> escribió:
> Gabriel Genellina wrote:
>> En Tue, 10 Jun 2008 09:44:13 -0300, Gabriel Rossetti
>> <gabriel.rossetti at arimaz.com> 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 :
>>> 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)
char x = some_word;
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')
accum = [0 for i in range(LAST-FIRST+1)]
x = some_word
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.
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