Signed zeros: is this a bug?

[Duncan Booth]

"Mark Dickinson" <dickinsm at gmail.com> wrote:

> I guess what's happening is that there's some optimization that avoids
> creating two separate float objects for a float literal that appears
> twice, and that optimization doesn't see the difference between 0. and
> -0. 

Don't guess. Test.

>>> def f():
	x = 0.0
	y = -0.0
	return x, y

>>> dis.dis(f)
  2           0 LOAD_CONST               1 (0.0)
              3 STORE_FAST               0 (x)

  3           6 LOAD_CONST               1 (0.0)
              9 STORE_FAST               1 (y)

  4          12 LOAD_FAST                0 (x)
             15 LOAD_FAST                1 (y)
             18 BUILD_TUPLE              2
             21 RETURN_VALUE        

Yes. Just the one constant there.


Tim Peters wrote in 
http://blog.gmane.org/gmane.comp.python.devel/day=20050409:

> All Python behavior in the presence of a NaN, infinity, or signed zero
> is a platform-dependent accident.  This is because C89 has no such
> concepts, and Python is written to the C89 standard.  It's not easy to
> fix across all platforms (because there is no portable way to do so in
> standard C), although it may be reasonably easy to fix if all anyone
> cares about is gcc and MSVC (every platform C compiler has its own set
> of gimmicks for "dealing with" these things).