Function(s) that downloads currency rate between PLN and the given currency in given date. Currencies are downloaded from The Polish National Bank site.

For example, if you need to know what was the currency rate between PLN and EUR in 2010-07-11 you can simply type:

>>> from datetime import date
>>> import nbp
>>> currency_data = nbp.download_exchange_rate(date(2010, 7, 11), 'EUR')
>>> assert currency_data == {
        'search_date': '2010-07-11',
        'table_no': u'132/A/NBP/2010',
        'pub_date': u'2010-07-09',
        'currency': {
            'name': u'euro',
            'rate': 4.0732999999999997,
            'code': u'EUR',
        },
    }

pub_date equals to 2010-07-09 because 2010-07-11 was not the working day, so the algorithm tryies to find first previous working day currency.

Polish National Bank (NBP) provides three types of currency tables: A, B and C. The module uses only A and B. The A table is published every working day and B table only on wednesdays.

The module first search for the currency in the A table, and if there is no results it searches B. It the date you provide doesn't have record in the tables, algtorithm searches for the first previous working day.

Result of the 'download_exchange_rate' algorithm is dictionary with following keys:

{ 'search_date': <date which was passed to the algorithm as string>,
  'table_no':    <nbp currency table no eg. '132/A/NBP/2010'>,
  'pub_date':    <publication date of table, it can be diffrent then 'search_date'>,
  'currency': {
      'name': <name of currency eg. u'euro'>,
      'rate': <value of the exchange rate>,
      'code': <currency code eg 'EUR' or 'USD'>
      }}

nosetest for tests

$ nosetests tests.py