This updates some of the sub unit values

[matthewsnell]

This fixes the issue #9
Values were taken from https://developers.facebook.com/docs/marketing-api/currencies/

[nickyr]

Hey! I really appreciate you taking the time to do this.

Of course, because currencies are a pain, Facebook's list and the list @shridharama provided in the original ticket don't agree on all currencies. I commented where I saw discrepancies.

Any thoughts from either of you about how we should address this? The ISO link may be more technically accurate, but the Facebook link may be more useful in practice. I'm sort of leaning towards using the mentality "Facebook knows more than me" and accepting all the proposed changes here, but I'd love input from others.

[nickyr]

Facebook might be wrong on this one. The link @shridharama provided and Wikipedia both indicate that 100 is correct.

[kaylafuchs]

It's possible Facebook isn't "wrong" here per se but is just setting arbitrary rules for the minimum allowed bid on their ad units, which sometimes matches up with established convention for that currency and sometimes doesn't (see here in the docs). In that case, if the sub unit isn't defunct we may want to go with the conventional usage as opposed to Facebook's rules. Thoughts?

[nickyr]

Ooh good find, @kaylafuchs. @matthewsnell, maybe we should leave Colombia and Costa Rica as they were and take your changes on the others?

[nickyr]

same here

[nickyr]

now for this one, the two lists disagree but Wikipedia says the sub unit is defunct, so maybe Facebook's is more accurate here

[kaylafuchs]

Was in Hungary this summer & did not ever encounter any denomination smaller than a Forint. Inflation is crazy there so it makes sense that the sub unit would be defunct. Based on those Facebook docs it looks like 1 indicates that there is no sub unit allowed, so it seems they actually agree here!

[nickyr]

here's another where wikipedia says the subunit is obsolete

[nickyr]

For this one, the lists disagree and wikipedia says the subunit is "rarely" used

[nickyr]

I'll definitely release this with a new major version

[matthewsnell]

I would probably lean more towards using Facebook's values as well.

[nickyr]

@shridharama @jcmanzo @kaylafuchs @DanayaMel @brendanpeters @lorenzocastillo I will merge this on Wednesday if nobody objects.

[kaylafuchs]

No objections here! I would be inclined to trust Facebook API docs over Wikipedia but it would be nice to have a more authoritative source for this kind of thing. 🤔

Edit: after looking more closely at those Facebook docs it seems that they're tweaking some currency rules in order to set the minimum allowed bid on their ad units. In that case we may not want to trust them.

[jcmanzo]

Looks like this never got merged. I'll take care of it later today..

[kaylafuchs]

@jcmanzo I think there's still an open question here about trusting the Facebook docs for Colombia and Costa Rica because they're using sub units to set a minimum allowed bid on their ad units - https://developers.facebook.com/docs/marketing-api/currencies/#example-offset-1

[suspectpart]

I guess the canonical source of truth here should be ISO 4217 which delineates currency designators, country codes and sub units. Wikipedia states:

ISO 4217 is a standard first published by International Organization for Standardization in 1978, which delineates currency designators, country codes (alpha and numeric), and references to minor units in three tables [...]. The ISO 4217 code list is used in banking and business globally. In many countries the ISO codes for the more common currencies are so well known publicly that exchange rates published in newspapers or posted in banks use only these to delineate the currencies, instead of translated currency names or ambiguous currency symbols. ISO 4217 codes are used on airline tickets and international train tickets to remove any ambiguity about the price.

Even when you encounter sub units rarely in some countries (e.g. for the Forint in Hungary), we should still stick to the Standard if it nominally allows sub units.

The latest version of the Standard was published on 29 August, 2018 and can be found here as an XML or XLS file.

I ran a small script that loads the XLS file, runs every currency through the CurrencyHelper and compares the sub units to the ones specified in the CurrencyHelper. These are the results:

ISO_4217 (Published 2018-08-29)
----------------
Can't process ANTARCTICA (No universal currency)
Can't process PALESTINE, STATE OF (No universal currency)
Can't process SOUTH GEORGIA AND THE SOUTH SANDWICH ISLANDS (No universal currency)
[BIF] expected 1, got 100
[CLF] expected 10000, got 100
[CLP] expected 1, got 100
[DJF] expected 1, got 100
[GNF] expected 1, got 100
[ISK] expected 1, got 100
[KMF] expected 1, got 100
[KRW] expected 1, got 100
[MGA] expected 100, got 5
[MRU] Currency Missing! (expected 100)
[PYG] expected 1, got 100
[RWF] expected 1, got 100
[STN] Currency Missing! (expected 100)
[UGX] expected 1, got 100
[UYI] expected 1, got 100
[UYW] Currency Missing! (expected 10000)
[VES] Currency Missing! (expected 100)
[VND] expected 1, got 10
[XAF] expected 1, got 100
[XAG] expected 'N.A.', got 100
[XAU] expected 'N.A.', got 100
[XBA] expected 'N.A.', got 100
[XBB] expected 'N.A.', got 100
[XBC] expected 'N.A.', got 100
[XBD] expected 'N.A.', got 100
[XDR] expected 'N.A.', got 100
[XOF] expected 1, got 100
[XPD] expected 'N.A.', got 100
[XPF] expected 1, got 100
[XPT] expected 'N.A.', got 100
[XSU] expected 'N.A.', got 100
[XTS] expected 'N.A.', got 100
[XUA] expected 'N.A.', got 100
[XXX] Currency Missing! (expected N.A.)

I would suggest to approach this as follows:

1. Discuss whether whether 100 is the correct sub units value for all X currencies (those are not real national currencies, but rather a mixture of supranational currencies and procedural purposes)
2. Provide the missing currencies

• [MRU] Currency Missing! (expected 100)
• [STN] Currency Missing! (expected 100)
• [UYW] Currency Missing! (expected 10000)
• [VES] Currency Missing! (expected 100)
  Be careful about MRU (Mauritanian ouguiya): This currency succeeds MRO and is one of two circulating currencies, along with the Malagasy ariary (MGA), whose division units are not based on a power of ten. The sub units here must also be 5. Note that in the ISO 4217 file, MRU and MGA are stated as sub units 2 (=100) but with a remark that it actually must be 1/5.)

3. Fix all currencies where the sub units differ from the ones stated in ISO 4217. That would be:

• [BIF] expected 1, got 100
• [CLF] expected 10000, got 100
• [CLP] expected 1, got 100
• [DJF] expected 1, got 100
• [GNF] expected 1, got 100
• [ISK] expected 1, got 100
• [KMF] expected 1, got 100
• [KRW] expected 1, got 100
• [PYG] expected 1, got 100
• [RWF] expected 1, got 100
• [UGX] expected 1, got 100
• [UYI] expected 1, got 100
• [VND] expected 1, got 10

If we implement these changes, we could add a remark to the README.md stating that py-money complies with ISO 4217, making it suitable for finance and business applications that need to comply with this Standard.

We could create an integration test that runs the ISO 4217 file through the CurrencyHelper to assert compliance. If it is ever going to change in the future, you just drop the new specification and get instant feedback about necessary adjustments.