Proposal: Fallback to defined operating_currency

[hlieberman]

Currently, when there's no currency defined at the transaction level or account level, we fall back to CURRENCY_NOT_CONFIGURED. While this is certainly the safest course of action, for csv importers in particular, this is likely to require a lot of redundant currency declarations in each importer.

Beancount already has the concept of an operating_currency, which we could reuse to act as a fallback currency. It seems likely to me that the average beancount user is likely to be using only a single currency, though I have no actual justification for this belief.

Thoughts? (I can easily write the patch to do this, but I didn't want to do so before checking the idea out.)

[redstreet]

I like this. Even though this may not be correct in 100% of the case, like you said, good design solves well for frequently used cases and results in an excellent out of the box experience. A patch would be welcome. We can call back on CURRENCY_NOT_CONFIGURED if operating_currency is not defined. Thank you!

[hlieberman]

I've been taking a look through how we can access the underlying beancount configuration, and unfortunately it doesn't look like there's a super good way to do it. I could do the same kind of ugly hack that is done in file_account using inspect -- but looking at the v3 branch of upstream, they've totally redone the configuration handling there. I think we should probably hold this feature back until after we've completed the v3 migration in #103.

[redstreet]

Ah yes, I forgot that we can't assume we have access to the beancount ledger from within the importer, as the ledger is not required for the import process.

Now I recall this is why I have the currency setup the way it is. My bad I didn't think of this when responding earlier, sorry!

FWIW, this is how my bean.import looks like:

def bank(importer, acct, config_overrides={}):
    account_number = acct[-4:]
    config = {
        'account_number'  : account_number,
        'main_account'    : acct,
        'currency'        : 'USD',
        'balance_assertion_date_type': 'last_transaction',
        }
    return apply_hooks(importer.Importer({**config, **config_overrides}), [PredictPostings()])

CONFIG = [
  bank(schwab, 'Assets:Bank:Schwab-xx0123'),
  ...
]

This way, the currency is set just once at the top.