Facundo Batista <facundobatista@gmail.com> wrote:
On Fri, Mar 19, 2010 at 5:50 PM, Guido van Rossum <guido@python.org> wrote:
As a downside, there is the worry that inadvertent mixing of Decimal and float can compromise the correctness of programs in a way that is hard to detect. But the anomalies above indicate that not fixing the
Decimal already has something that we can use in this case, and fits very nice here: Signals.
I like the simplicity of having a single signal (e.g. CoercionError), but a strictness context flag could offer greater control for people who only want pure decimal/integer operations. For example: strictness 0: completely promiscuous behaviour strictness 1: current py3k behaviour strictness 2: current py3k behaviour + pure equality comparisons strictness 3: current py3k behaviour + pure equality comparisons + disallow NaN equality comparisons [1] Just as an illustration, here is a quick and dirty diff using the DefaultContext for simplicity: Index: Lib/decimal.py =================================================================== --- Lib/decimal.py (revision 78352) +++ Lib/decimal.py (working copy) @@ -3765,8 +3765,8 @@ def __init__(self, prec=None, rounding=None, traps=None, flags=None, Emin=None, Emax=None, - capitals=None, _clamp=0, - _ignored_flags=None): + capitals=None, strictness=1, + _clamp=0, _ignored_flags=None): if flags is None: flags = [] if _ignored_flags is None: @@ -5785,7 +5785,9 @@ return other if isinstance(other, int): return Decimal(other) - if raiseit: + if isinstance(other, float) and DefaultContext.strictness == 0: + return Decimal.from_float(other) + if raiseit or DefaultContext.strictness > 1: raise TypeError("Unable to convert %s to Decimal" % other) return NotImplemented @@ -5800,7 +5802,8 @@ flags=[], Emax=999999999, Emin=-999999999, - capitals=1 + capitals=1, + strictness=1 ) Stefan Krah [1] See: http://mail.python.org/pipermail/python-dev/2009-November/093910.html, http://mail.python.org/pipermail/python-dev/2009-November/093952.html