This gist use the Yahoo web services to extract the currency rate for 1 USD.

usd_rates.py

#!/usr/bin/env python

from datetime import datetime
import json
from urllib import urlopen

YAHOO_CURRENCY_CONVERTER = 'http://finance.yahoo.com/connection/currency-converter-cache?date='

class CurrencyCoverterException(Exception):
    def __init__(self, value):
        self.value = value
    def __str__(self):
        return repr(self.value)


def get_json_currencies(date):
    """
    This method returns a json string containing a list of dict for each
    currency::
    
        {u'resource': {u'classname': u'Quote',
                        u'fields': {u'date': u'2010-02-01',
                                    u'price': u'0.71767',
                                    u'symbol': u'EUR=X',
                                    u'type': u'currency'}}}
    
    Note: of course the string returned by yahoo web service is not a valid json
    string so we need to do some uggly hack to transform it into one
    """
    string_cur = ('[' +
                  "".join(urlopen(YAHOO_CURRENCY_CONVERTER + date).readlines()[8:-5])
                                                             .replace("\n", "")
                  +']')
    currencies = json.loads(string_cur)
    if currencies:
        return currencies
    else:
        raise CurrencyCoverterException("The json string return by Yahoo WS is empty")

def extract_rate(currency, list_currencies):
    """
    
    """
    for cur in list_currencies:
        if cur['resource']['fields']['symbol'] == currency +'=X':
            return cur['resource']['fields']


if __name__ == '__main__':
    from optparse import OptionParser
    parser = OptionParser()
    
    parser.add_option("-d",
                      "--dates",
                      dest="dates",
                      help="Comma separated list of dates : yyyymmdd,yyyymmdd",
                      default=datetime.now().strftime('%Y%m%d')
                      )
    
    parser.add_option("-c",
                      "--currency",
                      dest="currency",
                      help="Currency you want the rate : EUR",
                      default="EUR"
                      )
    (options, args) = parser.parse_args()
    for date in options.dates.split(","):
        try:
            currencies = get_json_currencies(date)
            rate = extract_rate(options.currency, currencies)
            print rate['date'], 'theorique : ',rate['price'], 'banque : ', float(rate['price'])-0.03
        except CurrencyCoverterException as e:
            print "date %s : rate not available" %date