Gets you average NBP rate for given date and currency.

nbp-rates.py

#!/usr/bin/env python
"""
Get exchange rate from NBP service for USD (default) and provided day (or now)
"""

import argparse
from datetime import datetime

import requests


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


def get_exchangerate(date, currency):
    url = (f'http://api.nbp.pl/api/exchangerates/rates/a/{currency}/{date}/'
           f'?format=json')

    response = requests.get(url)

    if response.status_code != 200:
        return (f'No currency echange found for {date}, or there is a '
                f'problem with nbp.pl service '
                f'(returned {response.status_code}).')

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


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

    args = parser.parse_args()
    print(get_exchangerate(args.date, args.currency))


if __name__ == "__main__":
    main()