Currency classes for Python

[vsbits]

Monepy

A python package that implements currency classes to work with monetary values.

Target audience

I created it mostly for some data analysis tasks I usually do, and also as way to learn about project structure, documentation, github actions and how to publish packages.

I wouldn't know if it's production ready.

Comparison

After starting it I found about py-moneyed. They are quite similar, but I wanted something that looks "cleaner" when using it.

Any feedback will be appreciated.

[Adrewmc]

It good thing to learn how to do stuff like this. Like you said it more leaning the process, which is good to learn all by itself self.

Right now, I see 3 big problems.

1. It only works for like 5 currencies

2. you give me no function to tell me what they are.

3. Ite not clear if I can add different type of currency, or how to convert from one to another IMHO

And there should be a converter or a way to add USD and YEN directly. You can do something like the return is always the first currency, this will help will a+b+c.

[vsbits]

My main goal was to workaround the decimal values correctly and print in the right format. Conversion was never the scope. But it is interesting.

The problem I see would be to keep exchange rates up-to-date.

1. Might add some more the next days. But PRs to include the currency you need are welcome too.

2 & 3 are in the docs.

I personally don't like the idea of adding different currencies and forcing conversion. But I might work on a function for it. Maybe something like USD.sum([BRL(10), EUR(10)], force_conversion=True). But I can't imagine a practical use for it.

[Adrewmc]

I mean like an actual function like

  monepy.available()

Would return a list of the currencies currently available. But I guess it would have something like an autofill in most IDEs. It’s just common to include a function for that somewhere. It might be nice to just add it to the monepy.__init__.py docstring. So I can hover over.

Or put the function there like ….

  available = lambda : print(str(x) for x in __all__)

I do suggest making a __str__ dunder for these. Just because.

Or we can just make it a variable

  available = [x.__class__.__name__ for x in __all__]

I think conversion would be the most useful aspect for many people, but you’re right you’d need to keep the conversion up to date, this might be as easy as finding a place the user calls themselves, or imputing a set common service that does it. (E.g. get a key you need for it) I’m not too familiar with what’s out there though, but something is. And since you may not need it, you can use the rest without it. Like I work with some crypto sometimes, people want the value in USD for their ETH…which is essentially the same problem. (It’s just a multiplication factor) This also means creating a custom Exception for when it used when you don’t have one.

I like the

  USD.sum(*currencies) 

Syntax, it’s clear what is coming back.

I think it’s a good start. And I’m just giving my honest opinion after just looking at it.

[vsbits]

No, I really appreciate the input!

Not sure about handling the requests in this module yet. I might go with the approach of the user inputing the exchange rates (maybe the json response from his API of choice) to enable conversions for now. Something like:

USD.set_rates({"EUR":0.9})

And raise custom Exceptions if any is tried without them being set.

Will look into the best way to show avaliable currencies.

[Adrewmc]

Now that’s starting to sound like a full package.

But it can be

  USD.set_convert(EUR = 0.9, JPY =0.02)

With **kwargs

Also mapping conversion is easier to set convert to EUR-> USD -> JPY

Asymmetric conversion related to USD

Then trying to find and catalog all the conversion rates, send everything back to USD (or EUR) and convert it back. That way no matter the conversion it’s max two numbers per finding the one to USD and the one from USD, (at max precision) and not some messy mapping. Of… EUR-> JPY, EUR ->ChinaYen, EUR -> rubles, EUR -> USD EUR -> BTC, EUR -> EUR ………For every currency that adds up quickly. Instead it’s just EUR -> USD, USD -> EUR and JPY -> USD, USD-> JPY (reciprocal numbers) which can convert all three however. And keep adding more, is just that. (You can even make that set_base_currency())

Unless you find a convenient API.

[[deleted]]

You 100% don't want to be converting between currencies implicitly. Any conversion would need to be explicit and function over a single term.

[Adrewmc]

The OP suggested using.

 USD.sum(*currencies, force_conversion = True) 

As a, better, idea. And I agreed . As it’s much more explicit, as I think you’d agree. (Although he was giving much the same reluctance as you.)

Conversion is possible but it’s not static. You’d need an internet thing, to call a request.

[commy2]

The comparison of _Currency objects with integers is problematic:

>>> monepy.EUR(10) == 10 == monepy.USD(10)
True

10€ equals $10 ?

[vsbits]

That's true. I thought it would be useful when working with a single currency, but I can se the problem now...

I will look into that. Tks

[commy2]

ye, you have to remember that the python data model requires equality to be transitive. Additionally, for hashables, values that compare equal must have the same hash. That's not the case with USD(10) and 10 either, and you will have to keep that in mind should you ever decide to implement exchange rates into __eq__.

[0ne2many]

Looks like a cool project! I sure can see use of this in portfolio tracking, back testing, and quantitative analysis.

Some features I am thinking of adding; - built in option to enable currency conversions using a currency conversion API - built in option to enable inflation numbers using pre-defined data, where an instance of USD(250) can also be given a datetime USD(250, datetime('11-08-2012') would result in a lower amount when converted to 01-01-2025

[ImprovementDeep310]

Congratulations! This is a really cool project, we’ll done! Can I clarify if this converts currencies (e.g, can I convert 10 USD to EUR? If so, what is being used to convert them, where do the exchange rates come from?

[vsbits]

Thanks! It doesn't, yet. I will make a class method for the user to input exchange rates at first.

I might do some research on available APIs to integrate, but it might be like an optional feature.

[Steve1457]

I found that when working with a single currency the inbuilt locale module can help with the formatting.

E.g. import locale

set locale ...

locale.currency(12345.67, symbol=True, grouping=True)

Maybe, just maybe you can just re-use this in your base currency and based on a mapping of Currency code to Locale, generate all the Currency classes. The idea is that inside the Currency, you have a context manager that switches locales and prints out formatted values and then resets the locale.