'Returns the PriceCurrency object or none.
:param optional carrier: an int for the carrier.
:param optional region: an int for the region.
:param optional provider: an int for the provider. Defaults to bango.'

def get_price_currency(self, carrier=None, region=None, provider=None):

    from mkt.developers.providers import ALL_PROVIDERS
    provider = (provider or ALL_PROVIDERS[settings.DEFAULT_PAYMENT_PROVIDER].provider)
    if (not hasattr(Price, '_currencies')):
        Price.transformer([])
    lookup = price_key({'tier': self.id, 'carrier': carrier, 'provider': provider, 'region': region})
    try:
        price_currency = Price._currencies[lookup]
    except KeyError:
        return None
    return price_currency
