decimal

This is a Py2.3 implementation of decimal floating point arithmetic based on the General Decimal Arithmetic Specification:

and IEEE standard 854-1987:

Decimal floating point has finite precision with arbitrarily large bounds.

The purpose of this module is to support arithmetic using familiar “schoolhouse” rules and to avoid some of the 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
>>>

Functions

getcontext([_local]) Returns this thread’s context.
localcontext([ctx]) Return a context manager for a copy of the supplied context
setcontext(context[, _local]) Set this thread’s context to context.

Classes

Context([prec, rounding, traps, flags, ...]) Contains the context for a Decimal instance.
Decimal Floating point class for decimal arithmetic.
DecimalTuple

Exceptions

Clamped Exponent of a 0 changed to fit bounds.
ConversionSyntax Trying to convert badly formed string.
DecimalException Base exception class.
DivisionByZero Division by 0.
DivisionImpossible Cannot perform the division adequately.
DivisionUndefined Undefined result of division.
Inexact Had to round, losing information.
InvalidContext Invalid context.
InvalidOperation An invalid operation was performed.
Overflow Numerical overflow.
Rounded Number got rounded (not necessarily changed during rounding).
Subnormal Exponent < Emin before rounding.
Underflow Numerical underflow with result rounded to 0.