Python Decimal

decimal is a module providing utilities and APIs for working with fixed point and floating point numbers.

Usage

Decimal

A decimal.Decimal object can be instantiated with any of the following methods.

import decimal

decimal.Decimal('3.14')              #Decimal('3.14')
decimal.Decimal(3.14)                #Decimal('3.140000000000000124344978758017532527446746826171875')
decimal.Decimal((0, (3, 1, 4), -2))  #Decimal('3.14')

As demonstrated above, instantiating a decimal.Decimal object with a float is not likely to produce the desired result. When possible, construct numbers from strings. If an irrational number can be expressed as a fraction, compute it from decimal.Decimal objects.

d1 = decimal.Decimal(10)
d2 = decimal.Decimal(3)
d1 / d2                   #Decimal('3.3333333333333333333333333333')

There are also special values that can be instantiated like:

• decimal.Decimal('Infinity')

• decimal.Decimal('-Infinity')

• decimal.Decimal('NaN')

• decimal.Decimal('-0')

Contexts

Implicitly, decimal.Decimal objects inherit a set of behavior configurations from the active thread's context.

To examine or overwrite the active thread's context, use decimal.getcontext and decimal.setcontext. The object returned by decimal.getcontext is also directly writeable.

import decimal

decimal.getcontext()  #Context(prec=28,
                          rounding=ROUND_HALF_EVEN,
                          Emin=-999999,
                          Emax=999999,
                          capitals=1,
                          clamp=0,
                          flags=[],
                          traps=[Overflow, DivisionByZero, InvalidOperation])

getcontext().prec += 2

It is also possible to use a local context manager.

import decimal

with decimal.localcontext() as ctx:
    ctx.prec = 42
    d = decimal.Decimal(10) / decimal.Decimal(3)

# The unary `+` operator rounds `d` to the active thread's precision
+d

Constants

See also

Python decimal module documentation

Python Module of the Day article for decimal

CategoryRicottone