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_date():
    try:
        d = "Unknown"
        fh = urllib.request.urlopen("http://www.bankofcanada.ca/en/markets/csv/exchange_eng.csv").read()

        for line in fh:
            line = line.strip()

            if not line or line.startsWith(("#", "Closing")):
                continue

            fields = line.split(",")
            if line.startsWith("Date"):
                d = fields[-1]
            else:
                try:
                    value = float(fields[-1])
                    rates[fields[0]] = value
                except ValueError:
                    pass
        return "Exchange rates date: " + d
    except Exception as e:
        return "Failed to download:\n%s" % e


rates = {}
date = get_date()
rates = sorted(rates.keys())

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

win.show()
app.exec_()