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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_rate(self, currency, date):
 """Get the exchange rate for ``currency`` against ``_INTERNAL_CURRENCY`` If implementing your own backend, you should probably override :meth:`_get_rate()` rather than this. """

        if str(currency) == defaults.INTERNAL_CURRENCY:
            return Decimal(1)

        cached = cache.get(_cache_key(currency, date))
        if cached:
            return Decimal(cached)
        else:
            # Expect self._get_rate() to implement caching
            return Decimal(self._get_rate(currency, date))