Lack of Unit Pluralization and Decimalization of Significand (i.e.. 9.99999 instead of 10), despite Unit Conversion by Powers of 10

[OzborneOrteza]

When converting between units, such as:

• Meter to smaller units, such as millimeters: --output: 1000.0 millimeter
• Meter to larger units, such as yottameters: --output: 1.0000000000000001e-24 yottameter
• Meter to Custom SI extension prefixes (Quecca-/Quetta- (1030), Ronna- (1027), ronto- (10-27), quecto (10-30)) --output: 9.999999999999999e+29 quectometer

Often, the result is the conversion of "1" to "1.0000000000000001" or "9.999999999999999". This is undesirable, as it can cause error accumulation by floating point error. These do indeed accumulate, incrementing by the smallest place (ex: 1.0000000000000001 becomes 1.0000000000000002 when converting meters to Queccameters to Ronnameters).

I am just converting units that are powers of ten- the exponent should change, not the significand. Multiplying the measurement by a number, without changing the unit, does not cause this. Smaller magnitude (so units closer to unity) seem to return to scientific notation, but the error reappears when converting back to large units.

Additionally, units do not pluralize on output or print. However, units are converted into singular form on input.

Code is attached here: default_en.txt Unit Test Issues.txt

[dalito]

The imprecision is a consequence of using floats and how they are represented. Pint does not do anything special. You may use decimal numbers instead. In general, avoid unnecessary back-and-forth conversion. Just convert one time (or max. twice: input & output).

Because pint supports multiple languages, babel must be installed to generate output in plural-format, see

• https://pint.readthedocs.io/en/stable/tutorial.html?highlight=translate#localizing
• Code: https://pint.readthedocs.io/en/stable/_modules/pint/formatting.html?highlight=plural#

[OzborneOrteza]

Forgive me for my ignorance, but it would appear neither decimals nor fractions prevent the floating-point error. I've attached my code below, this time without any custom prefixes.

• Factions and Unit Testing.txt

Yes, I will no longer needlessly convert. But if I may- why might repeated conversion cause floating point error?

Ah, the Babel module makes sense! My bad!

[OrangeChannel]

Ah, full compatibility with Fraction and Decimals can be achieved by initializing the unit registry with non_int_type=decimal.Decimal etc... Change line 4 in the text you sent to ureg = UnitRegistry(non_int_type=Decimal) and that's it. You don't need to create quantities explicity with Decimal objects either once you do this, strings work too. So like ureg.Quantity('4.555 km') is sufficient enough to get a quantity who's magnitude is a Decimal('4.555').

[hgrecco]

As @OrangeChannel said. Feel free to reopen.