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Commit2450be6

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skirpichevrruuaanngStanFromIrelandhugovk
authored
decimal docs: specification link and examples (#128698)
Co-authored-by: RUANG (James Roy) <longjinyii@outlook.com>Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
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‎Doc/library/decimal.rst‎

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@@ -34,10 +34,12 @@ The :mod:`decimal` module provides support for fast correctly rounded
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decimal floating-point arithmetic. It offers several advantages over the
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:class:`float` datatype:
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* Decimal "is based on a floating-point model which was designed with people
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in mind, and necessarily has a paramount guiding principle -- computers must
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provide an arithmetic that works in the same way as the arithmetic that
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people learn at school." -- excerpt from the decimal arithmetic specification.
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* Decimal "is based on a `floating-point model
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<https://speleotrove.com/decimal/damodel.html#refnumber>`__ which was designed
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with people in mind, and necessarily has a paramount guiding principle --
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computers must provide an arithmetic that works in the same way as the
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arithmetic that people learn at school." -- excerpt from the decimal
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arithmetic specification.
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* Decimal numbers can be represented exactly. In contrast, numbers like
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``1.1`` and ``2.2`` do not have exact representations in binary
@@ -238,6 +240,26 @@ floating-point flying circus:
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>>>c% a
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Decimal('0.77')
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Decimals can be formatted (with:func:`format` built-in or:ref:`f-strings`) in
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fixed-point or scientific notation, using the same formatting syntax (see
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:ref:`formatspec`) as builtin:class:`float` type:
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..doctest::
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>>>format(Decimal('2.675'),"f")
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'2.675'
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>>>format(Decimal('2.675'),".2f")
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'2.68'
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>>>f"{Decimal('2.675'):.2f}"
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'2.68'
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>>>format(Decimal('2.675'),".2e")
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'2.68e+0'
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>>>with localcontext()as ctx:
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...ctx.rounding=ROUND_DOWN
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...print(format(Decimal('2.675'),".2f"))
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...
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2.67
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And some mathematical functions are also available to Decimal:
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>>>getcontext().prec=28

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