Gets you average NBP rate for given date and currency.

nbp-rates.py

#!/usr/bin/env python

import argparse
from datetime import datetime
import json
import requests

def date_type(s):
    try:
        return datetime.strptime(s, "%d-%m-%Y")
    except ValueError:
        msg = "Not a valid date: '{0}'.".format(s)
        raise argparse.ArgumentTypeError(msg)

parser = argparse.ArgumentParser(description='Gets average NBP rate for a '
                                             'given day.')
parser.add_argument('-d', '--date',
                    help="Date to get the rate - format DD-MM-YYYY. Today by "
                         "default.",
                    type=date_type)
parser.add_argument('-c', '--currency',
                    help="Currency code (ISO 4217). USD by default")

args = parser.parse_args()
d = args.date
c = args.currency


d = d or datetime.now()
c = c or 'USD'

url = ('http://api.nbp.pl/api/exchangerates/rates/a/%(c)s/%(d)s/?format=json'
       % {'c': c, 'd': d.strftime('%Y-%m-%d')})

response = requests.get(url)

print response.json()['rates'][0]['mid']