Genuine decimal numbers

Hi,

It may be worth pasting in some output from an example or two on this discussion post, just to show the difference, so people can more easily understand the benefits.

For instance, an error without the class, and the difference with it. I appreciate people could run the example code, but that entails them making the effort, and some people will not, unless they see some example output.

A minor point (perhaps worth it for a later code revision) could be to change the name of it, because decimal.py already exists for normal Python, and it may get confusing for people if they expect it to be the same (or similar) thing.

try this....

import decimal

decimal.Number(1) == decimal.Number(1.0)

one = decimal.Number(1)

two = decimal.Number(2)

eleven = decimal.Number(11)

pi = decimal.Number(3.1415)

minus_one = decimal.Number(-1)

print(decimal.add(one, two))

print(decimal.subtract(one, two))

print(decimal.multiply(eleven, two))

print(decimal.divide(one, eleven, 15))

print(decimal.absolute(minus_one))

print(decimal.integer(pi))

print(decimal.fraction(pi))

print(decimal.round(pi, 3))

# the correct way to express a = b

new_number = decimal.copy(one)

print(new_number)

Can you define precision and scale? Are precision and scale inferred by the constructors?

I mean, what is the output? Can you demonstrate the error without using the library, versus with using the library?

I was hoping, something like this (this isn't a real example, this is just to provide a rough idea of what I mean):

Without decimal-numbers library:

>>100 / 3

>> 33.330

With decimal-numbers library:

>>print(decimal.divide(decimal.integer(100), decimal.integer(3))

>> 33.3333333333

Also, are you using micropython with single-precision, or micropython with double-precision? I have not used micro:bit in a very long time, so I am not sure what it has by default (the micropython firmware is built for single or double precision, I just don't know which of the two the micro:bit firmware image is built to).

I just looked at your code on Github (with a view to answering Shabaz's questions)

You obviously want to share, which is great, but your code does not make it easy.

decimal.py is 945 lines of code with no comments or explanation other than:

#

Do you have some documents or notes that explain how it works and how it might be tweaked or modified or maintained ?

MK

They are implied by the precision of the factors in each function or creation of a new number, except division which you decare the precision.

On a microbit I performed 1/3 to 5000 places without running out of memory 

Have you looked at decimal_math.py or pi.py or the microbit versions microbit_root.py and microbit_pi.py

I have, They are examples of how ot use decimal.py but they don't explain how decimal.py is actually meant to work.

MK

On python 3 decimal.Number (0.115) != decimal.Number ("0.115") but on microbit they are the same.

It is only for version 2 microbit''s version 1 have a code limit of about 8kb

With the decimal numbers library try

decimal.divide(decimal.Number(100), decimal.Number(3), 1000)

The result will be 33.3333.....

A much greater precision than both python 3 and the 32 bit floats that are implemented in microbit micropython.

See examples of it in use in decimal_math.py and pi.py or for microbiology it's microbit_root.py and microbit_pi.py 

It just performs basic mathematics to a magnitude and precision only limited by memory, try

decimal.divide(decimal.Number(1), decimal.Number(3), 1000)