En Mon, 21 Jan 2008 17:36:29 -0200, Duncan Booth
<[EMAIL PROTECTED]> escribi�:
> Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> wrote:
>
>> On Mon, 21 Jan 2008 17:08:46 -0200, Gabriel Genellina wrote:
>>
>>> The future statement is another example, even worse:
>>>
>>> if 0:
>>> from __future__ import with_statement
>>>
>>> with open("xxx") as f:
>>> print f
>>
>> In Python >=2.5 it's a compile time error if that import is not the very
>> first statement in a source file.
>>
> That doesn't appear to be the case. With Python 2.5.1 the example
> Gabriel quoted will compile and run.
Yes, but now I've noticed that the 0 has some magic. The code above works
with 0, 0.0, 0j and ''. Using None, False, () or [] as the condition, will
trigger the (expected) syntax error.
Mmm, it may be the peephole optimizer, eliminating the dead branch. This
function has an empty body:
def f():
if 0: print "0"
if 0.0: print "0.0"
if 0j: print "0j"
if '': print "empty"
py> dis.dis(f)
5 0 LOAD_CONST 0 (None)
3 RETURN_VALUE
The other false values tested (False, None, () and []) aren't optimized
out.
--
Gabriel Genellina
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