How can I access the actual date and rate used when a fallback method is specified?

[rodrigogonegit]

Hey, I have a particular use case in which I'd like to save the last known date and rate for unknown values, to keep as a reference as to what actual rate and date were used.

def _use_last_known(self, currency):
        """Fill missing rates of a currency.
        This is done by using the last known rate.
        :param str currency: The currency to fill missing rates for.
        """
        rates = self._rates[currency]

        for date in sorted(rates):
            rate = rates[date]
            if rate is not None:
                last_rate, last_date = rate, date
            else:
                rates[date] = last_rate
                if self.verbose:
                    print(
                        "{}: filling {} missing rate using {} from {}".format(
                            currency, date, last_rate, last_date
                        )
                    )

It seems the lib is simply disregarding this information atm. I'd be happy to do it myself, but how would you like it to be done?

[alexprengere]

Indeed this information is not kept. If I understand correctly, what you want is a new method that for each currency and date, returns the actual date used for the rate?

Something like:

def _get_rate_actual_date(self, currency, date):
    pass

A possible implementation would be to fill a self._rates_origin[currency][date] -> origin_date object with those data. We would need to either fill it will all dates, or only the cases where a fallback was done. Also both fallback methods would need to be changed.

I am not 100% sure this is needed, as this is the first time such use case is mentioned, and it would grow a bit the memory usage (also, it can be implemented in client code using subclassing).