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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(currency):
 """Returns the rate from the default currency to `currency`."""

    source = get_rate_source()
    try:
        return Rate.objects.get(source=source, currency=currency).value
    except Rate.DoesNotExist:
        raise CurrencyConversionException(
            "Rate for %s in %s do not exists. "
            "Please run python manage.py update_rates" % (
                currency, source.name))