web_AI-5/django/didgeridoo/currencies/exchange_rates.py

from datetime import datetime
import urllib.request
import xml.etree.ElementTree as ET

"""
this method calls a rss/XML Resource
of Currency's and parses it to our
needed exchange rate values.
The return is a dictionary carring
Key:Value pairs of new currencys.
"""


def get_exchange_rate():
    # zweitweise kann die resource nicht geladen werden.
    # https://stackoverflow.com/a/43523497/4061870
    # During weekends there are no updates.
    # To develop i need a testresource.
    # In that case i comment the Online Resource block and uncomment the
    # development Block...

    # ~~~~~~~~~~~~~~~~~~~~~
    # Online Resource block:
    # ~~~~~~~~~~~~~~~~~~~~~
    today = datetime.now().strftime("%Y-%m-%d")
    SNB_URL = 'https://www.snb.ch/selector/de/mmr/exfeed/rss'
    urlsocket = ''
    try:
        urlsocket = urllib.request.urlopen(SNB_URL)
    except urllib.error.URLError as e:
        print('err: urllib.request.urlopen: ', e.reason)
    if urlsocket:
        root = ET.parse(urlsocket)
        root = ET.ElementTree(root)
        # ~~~~~~~~~~~~~~~~~~~~~
        # development block:
        # ~~~~~~~~~~~~~~~~~~~~~
        # today = "2018-01-08"
        # try:
        #     root = ET.ElementTree(file='rss')
        # except Exception as e:
        #     print('exchange_rates.py_urlsocket failed %s (
        #           %s) on date: %s for %s'
        #           % (e, type(e), root))
        # ~~~~~~~~~~~~~~~~~~~~~

        # Namespaces
        ns = {'rdf': 'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
              'none': 'http://purl.org/rss/1.0/',
              'dc': 'http://purl.org/dc/elements/1.1/',
              'dcterms': 'http://purl.org/dc/terms/',
              'cb': 'http://www.cbwiki.net/wiki/index.php/Specification_1.2/'
              }
        # Pathvariables to XML Namespaces
        rate_path = 'cb:statistics/cb:exchangeRate/'
        observation_path = 'cb:statistics/cb:exchangeRate/cb:observation/'
        exchange_rates = {}
        for item in root.findall('none:item', ns):
            # for eatch item n the list we grab the release date
            # to evaluate if its fresh data or old:

            # THE CURRENCY DATE:
            datetime_str = item.find('dc:date', ns).text
            # convert string to date object:
            # https://stackoverflow.com/a/12282040/4061870
            # seams like snb striked the microsecond somewhere
            # between Nov. and Dez. 2017 so maybe first check
            # time type is with milliseconds:
            try:
                date = datetime.strptime(''.join(
                             datetime_str.rsplit(':', 1)),
                             "%Y-%m-%dT%H:%M:%S%z").strftime(
                             "%Y-%m-%d")
            except Exception as e:
                print('%s (%s)' % (e, type(e)))
                try:
                    date = datetime.strptime(''.join(
                                 datetime_str.rsplit(':', 1)),
                                 "%Y-%m-%dT%H:%M:%S.%f%z").strftime(
                                 "%Y-%m-%d")
                    continue
                except Exception as e:
                    print('%s (%s)' % (e, type(e)))
                    continue
            # Print dates for development:
            # print("date:", date, "today:", today)
            # only the values of today are used so check for date in XML:
            if date == today:
                # now search for the currency exchange rate:
                target_currency = item.find(rate_path +
                                            'cb:targetCurrency', ns).text
                value = float(item.find(observation_path +
                                        'cb:value', ns).text)
                value = float(value)  # convert to float
                foreign_value = value  # copy to new value to have both.

                if item.find(observation_path + 'cb:unit_mult', ns) is None:
                    # because it's dangerous to check for present,
                    # i check for none here and have to set the target
                    # to 1. as im multiplying it later.
                    unit_mult = float("1.0")
                else:
                    # shift left by 2 digits with "/"
                    # https://stackoverflow.com/questions/8362792/
                    # because some currencys differ widly from CHF
                    unit_mult = item.find(observation_path +
                                          'cb:unit_mult', ns).text
                    # unit_mult defaults to '0' so we check for 8 decimal
                    # values (2..-6) they represent the fracton value to
                    # calculate the correct decimalpoint.
                    if unit_mult == '2':  # thinking of Bitcoins
                        unit_mult = '0.01'
                    if unit_mult == '1':
                        unit_mult = '0.10'
                    if unit_mult == '-1':
                        unit_mult = '10'
                    if unit_mult == '-2':  # Japan Yen
                        unit_mult = '100'
                    if unit_mult == '-3':
                        unit_mult = '1000'
                    if unit_mult == '-4':
                        unit_mult = '10000'
                    if unit_mult == '-5':
                        unit_mult = '100000'
                    if unit_mult == '-6':  # indian rupies
                        unit_mult = '1000000'
                    unit_mult = float(unit_mult)  # convert to float
                # calculate the Currency to CHF:
                foreign_value = 1 / value
                foreign_value *= unit_mult
                value = value / unit_mult
                # truncate it to decimal values provided by the xml:
                foreign_value_round = round(foreign_value, 5)
                # Print nice setup of all calculated currencys for development:
                # print("date:", date, " 1 ", target_currency, " costs: ",
                #       CHFvalue, "CHF and 1 ", base_currency, " costs: ",
                #       FOREIGNvalue_round, target_currency)
                exchange_rates.update(
                    {target_currency: foreign_value_round})
                # Print the Dictionary:
                # print(exchange_rates)
            else:
                continue
        return(exchange_rates, today)