The float conversion recipe is simpler in Py2.6
diff --git a/Doc/library/decimal.rst b/Doc/library/decimal.rst
index 7bf4494..37d2b35 100644
--- a/Doc/library/decimal.rst
+++ b/Doc/library/decimal.rst
@@ -1581,31 +1581,21 @@
A. Yes, all binary floating point numbers can be exactly expressed as a
Decimal. An exact conversion may take more precision than intuition would
-suggest, so trapping :const:`Inexact` will signal a need for more precision::
+suggest, so we trap :const:`Inexact` to signal a need for more precision::
- def floatToDecimal(f):
- "Convert a floating point number to a Decimal with no loss of information"
- # Transform (exactly) a float to a mantissa (0.5 <= abs(m) < 1.0) and an
- # exponent. Double the mantissa until it is an integer. Use the integer
- # mantissa and exponent to compute an equivalent Decimal. If this cannot
- # be done exactly, then retry with more precision.
+ def float_to_decimal(f):
+ "Convert a floating point number to a Decimal with no loss of information"
+ n, d = f.as_integer_ratio()
+ with localcontext() as ctx:
+ ctx.traps[Inexact] = True
+ while True:
+ try:
+ return Decimal(n) / Decimal(d)
+ except Inexact:
+ ctx.prec += 1
- mantissa, exponent = math.frexp(f)
- while mantissa != int(mantissa):
- mantissa *= 2.0
- exponent -= 1
- mantissa = int(mantissa)
-
- oldcontext = getcontext()
- setcontext(Context(traps=[Inexact]))
- try:
- while True:
- try:
- return mantissa * Decimal(2) ** exponent
- except Inexact:
- getcontext().prec += 1
- finally:
- setcontext(oldcontext)
+ >>> float_to_decimal(math.pi)
+ Decimal("3.141592653589793115997963468544185161590576171875")
Q. Why isn't the :func:`floatToDecimal` routine included in the module?