def medium_rate
      regexp = Regexp.new("#{currency_code} / PLN")
      page.search("//span[@name='pair']").each do |td|
        if (regexp.match(td.content))
          return td.next_element.content.to_f
        end
      end
    end
def medium_rate
      regexp = Regexp.new("#{currency_code} / PLN")
      page.search("//span[@name='pair']").each do |td|
        if (regexp.match(td.content))
          return td.next_element.content.to_f
        end
      end
    end
Constructor method.
 Initializes the following:
 * a url of the source
 * and the name of the source
 * a list of currency codes available
 Fetch medium rate which is calculated based on current transactions in Walutomat