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Entry for decimal and fractions.

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Raymond Hettinger 2010-12-15 22:35:03 +00:00
parent 480ed78c0e
commit 07a605b1c7
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Doc/whatsnew/3.2.rst
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@ -419,14 +419,6 @@ Some smaller changes made to the core Python language are:
(Added by Antoine Pitrou; :issue:`9757`.) (Added by Antoine Pitrou; :issue:`9757`.)
* Mark Dickinson crafted an elegant and efficient scheme for assuring that
different numeric datatypes will have the same hash value whenever their
actual values are equal::
>>> assert hash(Fraction(3, 2)) == hash(1.5) == \
hash(Decimal("1.5")) == hash(complex(1.5, 0))
(See :issue:`8188`.)
* Previously it was illegal to delete a name from the local namespace if it * Previously it was illegal to delete a name from the local namespace if it
occurs as a free variable in a nested block:: occurs as a free variable in a nested block::
@ -773,6 +765,43 @@ way to return a logging instance for use in the body of enclosed statements.
(Contributed by Michael Foord in :issue:`9110`.) (Contributed by Michael Foord in :issue:`9110`.)
decimal and fractions
---------------------
Mark Dickinson crafted an elegant and efficient scheme for assuring that
different numeric datatypes will have the same hash value whenever their actual
values are equal (:issue:`8188`)::
>>> assert hash(Fraction(3, 2)) == hash(1.5) == \
hash(Decimal("1.5")) == hash(complex(1.5, 0))
An early decision to limit the inter-operability of various numeric types has
been relaxed. It is still unsupported (and ill-advised) to to have implicit
mixing in arithmetic expressions such as ``Decimal('1.1') + float('1.1')``
because the latter loses information in the process of constructing the binary
float. However, since existing floating point value can be converted losslessly
to either a decimal or rational representation, it makes sense to add them to
the constructor and to support mixed-type comparisons.
* The :class:`decimal.Decimal` contructor now accepts :class:`float` objects
directly so there in no longer a need to use the :meth:`~decimal.Decimal.from_float`
method.
* Mixed type comparisons are now fully supported so that
:class:`~decimal.Decimal` objects can be directly compared with :class:`float`
and :class:`fractions.Fraction`.
Similar changes were made to :class:`fractions.Fraction` so that the
:meth:`~fractions.Fraction.from_float()` and :meth:`~fractions.Fraction.from_decimal`
methods are no longer needed.
Another useful change for the :mod:`decimal` module is that the
:attr:`Context.clamp` attribute is now public. This is useful in creating
contexts that correspond to the decimal interchange formats specified in IEEE
754 (see :issue:`8540`).
(Contributed by Mark Dickinson.)
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