<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def convert_currency(self, base_fiat, base_amount, target_fiat):
 """ Convert one fiat amount to another fiat. Uses the fixer.io service. """

        url = "http://api.fixer.io/latest?base=%s" % base_fiat
        data = self.get_url(url).json()
        try:
            return data['rates'][target_fiat.upper()] * base_amount
        except KeyError:
            raise Exception("Can not convert %s to %s" % (base_fiat, target_fiat))