[New-bugs-announce] [issue11128] decimal.py: to_integral() corner cases

[Stefan Krah]

New submission from Stefan Krah <stefan-usenet at bytereef.org>:

Hi,

to_integral() should behave like quantize() for negative exponents:

"Otherwise (the operand has a negative exponent) the result is the
 same as using the quantize operation using the given operand as the
 left-hand-operand, 1E+0 as the right-hand-operand, and the precision
 of the operand as the precision setting. The rounding mode is taken
 from the context, as usual."


There are some corner cases where this matters:


>>> from decimal import *
>>> c = Context(prec=1, Emin=-1, Emax=1, traps=[])
>>> d = Context(prec=4, Emin=-1, Emax=1, traps=[])
>>> 
>>> c.to_integral(Decimal("999.9"))
Decimal('1000')
>>> d.quantize(Decimal("999.9"), Decimal("1e0"))
Decimal('NaN')


Indeed, decNumber returns NaN for to_integral(). This is an odd
situation, since for the result it is possible to exceed the
precision but not Emax:


>>> c = Context(prec=3, Emin=-3, Emax=3, traps=[])
>>> d = Context(prec=4, Emin=-3, Emax=3, traps=[])
>>> c.to_integral(Decimal("999.9"))
Decimal('1000')
>>> d.quantize(Decimal("999.9"), Decimal("1e0"))
Decimal('1000')


The specification is on the side of decNumber, but I wonder if this is
an oversight.

----------
components: Library (Lib)
messages: 127986
nosy: mark.dickinson, skrah
priority: normal
severity: normal
status: open
title: decimal.py: to_integral() corner cases
type: behavior
versions: Python 3.3

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue11128>
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