`decimal`

Exact decimal numbers: decimal.of("0.1").add("0.2") is exactly 0.3, where plain numbers give 0.30000000000000004. Use them for money and anything that is counted in decimal places. A decimal has .text (what it shows), .number (nearest plain number) and methods add, sub, mul, div, round, compare, equals, abs, negate, is_zero; decimal.sum() adds a list. Arithmetic keeps 34 significant digits.

import decimal

Example

import decimal

say(0.1 + 0.2)
say(decimal.of("0.1").add("0.2").text)
let price = decimal.of("19.99")
say(price.mul(3).text, price.mul("1.18").round(2).text)
say(decimal.sum(["1.10", "2.20", "3.30"]).text)

Functions

of(value)

returns decimal

An exact decimal from text like "19.99", a number, or another decimal. Text keeps every digit ("1.50" stays 1.50); a plain number is read the way it prints (0.1 becomes exactly 0.1).

Visualizehow decimal.of works

decimal.of("1.50") gives 1.5

value"1.50"

Real result: worked out by running this example with TB while the site was built.

is_decimal(x)

returns bool

True if x came from the decimal library.

Visualizehow decimal.is_decimal works

decimal.is_decimal(decimal.of("1")) gives true

xdecimal.of("1")

Real result: worked out by running this example with TB while the site was built.

add(a, b)

returns decimal

a + b exactly: decimal.add("0.1", "0.2").text is "0.3".

Visualizehow decimal.add works

decimal.add("0.1", "0.2").text gives "0.3"

b0.2

Real result: worked out by running this example with TB while the site was built.

sub(a, b)

returns decimal

a - b exactly.

Visualizehow decimal.sub works

decimal.sub("1.00", "0.35").text gives "0.65"

Real result: worked out by running this example with TB while the site was built.

mul(a, b)

returns decimal

a * b exactly.

Visualizehow decimal.mul works

decimal.mul("19.99", 3).text gives "59.97"

Real result: worked out by running this example with TB while the site was built.

div(a, b)

returns decimal

a / b to 34 significant digits. Error on division by zero.

Visualizehow decimal.div works

decimal.div("1", "3").text gives "0.3333333333333333333333333333333333"

b3

Real result: worked out by running this example with TB while the site was built.

round(value, places, mode?)

returns decimal

Round to that many decimal places: decimal.round("2.675", 2).text is "2.68" with mode "half_up" (default "half_even" rounds ties to the even digit, like banks do).

Visualizehow decimal.round works

decimal.round("2.675", 2, "half_up").text gives "2.68"

modehalf_up

Real result: worked out by running this example with TB while the site was built.

compare(a, b)

returns number

-1 if a < b, 0 if equal, 1 if a > b. Handy for sort_by.

Visualizehow decimal.compare works

decimal.compare("1.5", "1.50") gives 0

b1.50

Real result: worked out by running this example with TB while the site was built.

sum(values, ...)

returns decimal

Add up a list of decimals, numbers or texts exactly: decimal.sum(["0.1", "0.2", 0.3]).text is "0.6".

Visualizehow decimal.sum works

decimal.sum(["0.1", "0.2", 0.3]).text gives "0.6"

Real result: worked out by running this example with TB while the site was built.

text(value)

returns text

A decimal (or number) as plain digits: decimal.text(1e21) has no exponent.

Visualizehow decimal.text works

decimal.text(1e21) gives "1000000000000000000000"

value1e21

Real result: worked out by running this example with TB while the site was built.

number(value)

returns number

The nearest plain number for a decimal.

Visualizehow decimal.number works

decimal.number(decimal.of("19.99")) gives 19.99

Real result: worked out by running this example with TB while the site was built.

money(value, places?, mode?)

returns text

Round like money and show with thousands separators and fixed places: decimal.money("1234.5") is "1,234.50". places defaults to 2, mode to "half_up".

Visualizehow decimal.money works

decimal.money("1234.5", 2) gives "1,234.50"

places2

Real result: worked out by running this example with TB while the site was built.

Values

Name	Value	What it is
`decimal.precision`	`34`	How many significant digits arithmetic keeps (34). Visualizehow decimal.precision works `decimal.precision` gives `34` No inputs: call it as it is. Real value, read from TB while the site was built.
`decimal.modes`	`["half_even", "half_up", "half_down", "up", "down", "ceiling", "floor"]`	The rounding modes round() accepts. Visualizehow decimal.modes works `decimal.modes` gives `["half_even", "half_up", "half_down", "up", "down", "ceiling", "floor"]` No inputs: call it as it is. Real value, read from TB while the site was built.