This is a Py2.3 implementation of decimal floating point arithmetic based on the General Decimal Arithmetic Specification:
www2.hursley.ibm.com/decimal/decarith.html
www.cs.berkeley.edu/~ejr/projects/754/private/drafts/854-1987/dir.html
Decimal floating point has finite precision with arbitrarily large bounds.
The purpose of the module is to support arithmetic using familiar "schoolhouse" rules and to avoid the some of tricky representation issues associated with binary floating point. The package is especially useful for financial applications or for contexts where users have expectations that are at odds with binary floating point (for instance, in binary floating point, 1.00 % 0.1 gives 0.09999999999999995 instead of the expected Decimal("0.00") returned by decimal floating point).
Here are some examples of using the decimal module:
>>> from decimal import >>> setcontext(ExtendedContext) >>> Decimal(0) Decimal("0") >>> Decimal("1") Decimal("1") >>> Decimal("-.0123") Decimal("-0.0123") >>> Decimal(123456) Decimal("123456") >>> Decimal("123.45e12345678901234567890") Decimal("1.2345E+12345678901234567892") >>> Decimal("1.33") + Decimal("1.27") Decimal("2.60") >>> Decimal("12.34") + Decimal("3.87") - Decimal("18.41") Decimal("-2.20") >>> dig = Decimal(1) >>> print dig / Decimal(3) 0.333333333 >>> getcontext().prec = 18 >>> print dig / Decimal(3) 0.333333333333333333 >>> print dig.sqrt() 1 >>> print Decimal(3).sqrt() 1.73205080756887729 >>> print Decimal(3) 123 4.85192780976896427E+58 >>> inf = Decimal(1) / Decimal(0) >>> print inf Infinity >>> neginf = Decimal(-1) / Decimal(0) >>> print neginf -Infinity >>> print neginf + inf NaN >>> print neginf inf -Infinity >>> print dig / 0 Infinity >>> getcontext().traps[DivisionByZero] = 1 >>> print dig / 0 Traceback (most recent call last): ... ... ... DivisionByZero: x / 0 >>> c = Context() >>> c.traps[InvalidOperation] = 0 >>> print c.flags[InvalidOperation] 0 >>> c.divide(Decimal(0), Decimal(0)) Decimal("NaN") >>> c.traps[InvalidOperation] = 1 >>> print c.flags[InvalidOperation] 1 >>> c.flags[InvalidOperation] = 0 >>> print c.flags[InvalidOperation] 0 >>> print c.divide(Decimal(0), Decimal(0)) Traceback (most recent call last): ... ... ... InvalidOperation: 0 / 0 >>> print c.flags[InvalidOperation] 1 >>> c.flags[InvalidOperation] = 0 >>> c.traps[InvalidOperation] = 0 >>> print c.divide(Decimal(0), Decimal(0)) NaN >>> print c.flags[InvalidOperation] 1 >>>