On Thu, Mar 5, 2020 at 5:55 AM André Roberge <andre.roberge@gmail.com> wrote:

On Thu, Mar 5, 2020 at 5:29 AM Steve Barnes <GadgetSteve@live.co.uk> wrote:

One of the lovely things about Python is that we have the capability to avoid issues such as the vagaries of the floating point type with libraries such as decimal and fractions. This is wonderous to me but comes with an issue that I suspect is limiting its usage. That issue is that you have to litter your code with constructors of those types, e.g.

 

SNIP

 

Wouldn’t it be possible to have something along the lines of:

 

```

from decimal import TreatFloatsAsDecimal

@TreatFloatsAsDecimal

a = 0.1  # These are all now decimals

b = 0.2

c = 0.3

a + b == c # This now works

```

It is possible, and quite straightforward, to do this as an import hook or a custom encoding. I will try to do so and document it later today, and post it on this list.

Quick **first draft**:

    >>> from ideas.examples import decimal_math

    >>> hook = decimal_math.add_hook()
    >>> from ideas import console
    >>> console.start()
    Configuration values for the console:
        source_init from ideas.examples.decimal_math
        transform_source from ideas.examples.decimal_math
    --------------------------------------------------
    Ideas Console version 0.0.15. [Python version: 3.7.3]

    ~>> 0.1 + 0.2 == 0.3
    True
    ~>> 0.1 * 10 == 1
    True
    ~>> 0.1
    Decimal('0.1')
    ~>> 0.1 + 0.100

    Decimal('0.200')

Documentation at https://aroberge.github.io/ideas/docs/html/decimal_math.html   (This took longer to write than the actual code.)

André Roberge

 

 

I do know that this goes against the explicit is better than implicit so an alternative might be to have a flexible base modifier, something like:

```

from decimal import DecimalBase as D

 

a = 0D0.1  # These are all now decimals

b = 0D0.2

c = 0D0.3

a + b == c # This now works

```

 

Since anything like this would require overriding at least part of the base interpreter I do not think that this is a suitable one for an external PyPi library or at least some hooks in the interpreter would be required to make it possible.

 

Any thoughts, feedback, interest, expressions of horror? Or is this already there and I have missed it?

 

Steve Barnes

 

 

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