pyQt: eg3

import sys
import urllib2
from PyQt4 import QtCore
from PyQt4 import QtGui

class Form(QtGui.QDialog):
    def __init__(self, parent=None):
        super(Form, self).__init__(parent)

        date = self.getdata()
        rates = sorted(self.rates.keys())

        dateLabel = QtGui.QLabel(date)
        self.fromComboBox = QtGui.QComboBox()
        self.fromComboBox.addItems(rates)
        self.fromSpinBox = QtGui.QDoubleSpinBox()
        self.fromSpinBox.setRange(0.01, 10000000.00)
        self.fromSpinBox.setValue(1.00)
        self.toComboBox = QtGui.QComboBox()
        self.toComboBox.addItems(rates)
        self.toLabel = QtGui.QLabel("1.00")

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

        self.connect(self.fromComboBox,
            QtCore.SIGNAL("currentIndexChanged(int)"), self.updateUi)
        self.connect(self.toComboBox,
            QtCore.SIGNAL("currentIndexChanged(int)"), self.updateUi)
        self.connect(self.fromSpinBox,
            QtCore.SIGNAL("valueChanged(double)"), self.updateUi)
        self.setWindowTitle("Currency")

    def updateUi(self):
        to = unicode(self.toComboBox.currentText())
        from_ = unicode(self.fromComboBox.currentText())
        amount = ((self.rates[from_] / self.rates[to]) *
                  self.fromSpinBox.value())
        self.toLabel.setText("{0:.2f}".format(amount))

    def getdata(self): # Idea taken from the Python Cookbook
        self.rates = {}
        try:
            date = "Unknown"
            fh = urllib2.urlopen("http://www.bankofcanada.ca"
                                 "/en/markets/csv/exchange_eng.csv")
            for line in fh:
                line = line.rstrip()
                if not line or line.startswith(("#", "Closing ")):
                    continue
                fields = line.split(",")
                if line.startswith("Date "):
                    date = fields[-1]
                else:
                    try:
                        value = float(fields[-1])
                        self.rates[unicode(fields[0])] = value
                    except ValueError:
                        pass
            return "Exchange Rates Date: " + date
        except Exception, e:
            return "Failed to download:\n{0}".format(e)    

app = QtGui.QApplication(sys.argv)
form = Form()
form.show()
app.exec_()