Retrieve exchange rates from Central Bank of Ireland and load them into a dictionary

ExchangeRates.py

# -*- coding: utf-8 -*-
import urllib
import xlrd

class ExchangeRates():
    """ 
    Class to fetch exchange rate information from the Central Bank of Ireland

    Example:
    
        ex = ExchangeRates()
        latest_rates = ex.get_latest_rates()
        if latest_rates:
            for rate in latest_rates:
                print rate, latest_rates[rate]
        else:
            print ex.error

    """

    url, workbook, error = None, None, None

    def __init__(self, url=None):
        self.url = 'http://www.centralbank.ie/polstats/stats/exrates/Documents/Past%205%20days.xls'
        if url:
            self.url = url

    def get_latest_rates(self):
        """ Def to open and retreive rate information and
        place into dict"""

        xls_file = self.download_file()
        if not xls_file:
            return False

        try:
            self.workbook = xlrd.open_workbook(xls_file)
        except Exception, e:
            self.error = 'Failed to retreive data from central bank'
            return False

        worksheet = self.workbook.sheet_by_index(0)
        num_rows = worksheet.nrows - 1
        num_cells = worksheet.ncols - 1

        rates, current_row = {}, 0
        latest_date = worksheet.cell_value(0,6)
        latest_rate = 6

        while current_row < num_rows:
            current_row += 1
            rates[worksheet.cell_value(current_row,0)] = worksheet.cell_value(current_row,6)

        return rates

    def download_file(self):
        excel_file = urllib.URLopener()
        try:
            excel_file.retrieve(self.url, '/tmp/exchange_rates.xls')
            return '/tmp/exchange_rates.xls'
        except Exception, e:
            self.error = 'Failed to retreive exchange rate file'
            return False

It would be nice if the exchange rate file contained the currency code like the european central bank.