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109 lines
2.7 KiB
109 lines
2.7 KiB
"""Decimal fixed-point and floating-point arithmetic.
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This is an implementation of decimal floating-point arithmetic based on
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the General Decimal Arithmetic Specification:
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http://speleotrove.com/decimal/decarith.html
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and IEEE standard 854-1987:
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http://en.wikipedia.org/wiki/IEEE_854-1987
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Decimal floating point has finite precision with arbitrarily large bounds.
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The purpose of this module is to support arithmetic using familiar
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"schoolhouse" rules and to avoid some of the tricky representation
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issues associated with binary floating point. The package is especially
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useful for financial applications or for contexts where users have
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expectations that are at odds with binary floating point (for instance,
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in binary floating point, 1.00 % 0.1 gives 0.09999999999999995 instead
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of 0.0; Decimal('1.00') % Decimal('0.1') returns the expected
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Decimal('0.00')).
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Here are some examples of using the decimal module:
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>>> from decimal import *
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>>> setcontext(ExtendedContext)
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>>> Decimal(0)
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Decimal('0')
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>>> Decimal('1')
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Decimal('1')
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>>> Decimal('-.0123')
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Decimal('-0.0123')
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>>> Decimal(123456)
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Decimal('123456')
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>>> Decimal('123.45e12345678')
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Decimal('1.2345E+12345680')
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>>> Decimal('1.33') + Decimal('1.27')
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Decimal('2.60')
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>>> Decimal('12.34') + Decimal('3.87') - Decimal('18.41')
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Decimal('-2.20')
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>>> dig = Decimal(1)
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>>> print(dig / Decimal(3))
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0.333333333
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>>> getcontext().prec = 18
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>>> print(dig / Decimal(3))
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0.333333333333333333
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>>> print(dig.sqrt())
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1
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>>> print(Decimal(3).sqrt())
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1.73205080756887729
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>>> print(Decimal(3) ** 123)
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4.85192780976896427E+58
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>>> inf = Decimal(1) / Decimal(0)
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>>> print(inf)
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Infinity
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>>> neginf = Decimal(-1) / Decimal(0)
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>>> print(neginf)
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-Infinity
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>>> print(neginf + inf)
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NaN
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>>> print(neginf * inf)
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-Infinity
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>>> print(dig / 0)
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Infinity
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>>> getcontext().traps[DivisionByZero] = 1
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>>> print(dig / 0)
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Traceback (most recent call last):
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...
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...
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...
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decimal.DivisionByZero: x / 0
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>>> c = Context()
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>>> c.traps[InvalidOperation] = 0
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>>> print(c.flags[InvalidOperation])
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0
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>>> c.divide(Decimal(0), Decimal(0))
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Decimal('NaN')
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>>> c.traps[InvalidOperation] = 1
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>>> print(c.flags[InvalidOperation])
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1
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>>> c.flags[InvalidOperation] = 0
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>>> print(c.flags[InvalidOperation])
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0
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>>> print(c.divide(Decimal(0), Decimal(0)))
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Traceback (most recent call last):
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...
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...
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...
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decimal.InvalidOperation: 0 / 0
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>>> print(c.flags[InvalidOperation])
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1
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>>> c.flags[InvalidOperation] = 0
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>>> c.traps[InvalidOperation] = 0
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>>> print(c.divide(Decimal(0), Decimal(0)))
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NaN
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>>> print(c.flags[InvalidOperation])
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1
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>>>
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"""
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try:
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from _decimal import *
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from _decimal import __version__
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from _decimal import __libmpdec_version__
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except ImportError:
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import _pydecimal
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import sys
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_pydecimal.__doc__ = __doc__
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sys.modules[__name__] = _pydecimal
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