exchange.py

##################################################
# Benjamin Grant
"""
requests (http://docs.python-requests.org/en/master/) by Kenneth Reitz used for retrieving data from the web
The idea for this module is from Codio Week 1. The use of XML ElementTree also derived from there, however the logic was entirely created myself with help from https://docs.python.org/2/library/xml.etree.elementtree.html
"""
import requests
import xml.etree.ElementTree as ET

# Returns a dictionary of currencies and rates
async def getCurrencyDictionary():
  # Use of a context manager taken from http://docs.python-requests.org/en/master/api/#request-sessions
  with requests.Session() as r:
    response = r.get("http://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml").text
    
  root = ET.fromstring(response)
  curr={}
  for child in root[2][0]:
    curr[child.attrib["currency"]] = float(child.attrib["rate"])
  curr["EUR"] = 1
  curr["XDR"] = 1/(0.423 + 12.1*(1/curr["JPY"]) + 0.111*(1/curr["GBP"]) + 0.66*(1/curr["USD"]))
  return curr
  
  
async def convertCurrency(to, base, amount):
  
  if amount <= 0:
    return amount
  
  currencies =  await getCurrencyDictionary()
  return amount*currencies[to]/currencies[base]
##################################################