from PySide.QtGui import *
import urllib.request
import sys


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

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

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

        grid = QGridLayout()
        grid.addWidget(self.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.fromComboBox.currentIndexChanged().connect(self.update_ui)
        self.toComboBox.currentIndexChanged().connect(self.update_ui)
        self.fromSpinBox.valueChanged().connect(self.update_ui)

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

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

    def get_date(self):
        try:
            date = "Unknown"

            fh = urllib.request.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[fields[0]] = value
                    except ValueError:
                        pass
            return "Exchange rates date: " + date
        except Exception as e:
            return "Failed to download:\n%s" % e


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


=========================


Traceback (most recent call last):
  File "C:xxx/main.py", line 70, in <module>
    form = Form()
  File "C:xxx/main.py", line 32, in __init__
    self.fromComboBox.currentIndexChanged().connect(self.update_ui)
TypeError: native Qt signal is not callable

Process finished with exit code 1