if(debug), optimized away?

[Bengt Richter]

On Thu, 25 Jul 2002 20:39:32 +0200, Yigal Duppen <yduppen at xs4all.nl> wrote:

>> if(debug):
>>    if(items > 9):
>>      print "fatal error..."
>>    do_some_check_foo(42)
>>    ...
>>
>> If I set debug=0, is this code optimized away as in most
>> C/C++?? compilers?
>
>I doubt it.
>However, if you use the (predefined) __debug__, it does get optimized away 
>(at least, I think so).
>
>if __debug__:
>        # do stuff
>
>Note that you cannot set __debug__; it is always true, except when running 
>python with the -O flag.
>
 You are right:
 [14:09] C:\pywk\junk>python -O
 Python 2.2 (#28, Dec 21 2001, 12:21:22) [MSC 32 bit (Intel)] on win32
 Type "help", "copyright", "credits" or "license" for more information.
 >>> __debug__
 0
 >>> __debug__=1
   File "<stdin>", line 1
 SyntaxError: can not assign to __debug__
 >>> from miscutil import disex
 >>> disex("""\
 ... if __debug__:
 ...    a='debug'
 ... else:
 ...    a='no debug'
 ... """)
           0 LOAD_CONST               0 ('no debug')
           3 STORE_NAME               0 (a)
           6 LOAD_CONST               1 (None)
           9 RETURN_VALUE

(disex is just a convenience thing of mine using compile and dis)

>Furthermore, for checks such as these it is better to use the 'assert' 
>keyword. This too is removed when python -O is used.
>
>assert items > 9, "Fatal error, too many items"
>

Regards,
Bengt Richter