import codecs
import csv
import sys
import urllib.request

from PySide.QtCore import Slot
from PySide.QtGui import *


app = QApplication(sys.argv)
win = QWidget()
win.setWindowTitle('Test Window')


@Slot()
def update_ui():
    to = toComboBox.currentText()
    from_ = fromComboBox.currentText()

    amount = (rates[from_] / rates[to]) * fromSpinBox.value()
    toLabel.setText("%0.2f" % amount)


def get_rates():
    d = "Unknown"
    url_string = "http://www.bankofcanada.ca/en/markets/csv/exchange_eng.csv"
    raw_file = urllib.request.urlopen(url_string)
    decoded_file = codecs.getreader("utf-8")(raw_file)
    rows = csv.reader(decoded_file)

    for row in rows:
        if not row or row[0].startswith("#"):
            continue

        if row[0].startswith("Date "):
            d = row[-1]
        else:
            try:
                value = float(row[-1])
                rates[row[0]] = value
            except ValueError:
                pass
    return "Exchange rates date: " + d


rates = {}
date = get_rates()

dateLabel = QLabel(date)
fromComboBox = QComboBox()
fromComboBox.addItems(sorted(rates.keys()))
fromSpinBox = QDoubleSpinBox()
fromSpinBox.setRange(0.01, 100000000.00)
fromSpinBox.setValue(1.00)
toComboBox = QComboBox()
toComboBox.addItems(sorted(rates.keys()))
toLabel = QLabel("1.00")

grid = QGridLayout()
grid.addWidget(dateLabel, 0, 0)
grid.addWidget(fromComboBox, 1, 0)
grid.addWidget(fromSpinBox, 1, 1)
grid.addWidget(toComboBox, 2, 0)
grid.addWidget(toLabel, 2, 1)
win.setLayout(grid)

fromSpinBox.valueChanged.connect(update_ui)

win.show()
app.exec_()