Traceback (most recent call last):
  File "/main.py", line 70, in <module>
    form = Form()
  File "/main.py", line 32, in __init__
    self.fromComboBox.currentIndexChanged.connect(self.update_ui())
  File "/main.py", line 40, in update_ui
    amount = (self.rates[from_] / self.rates[to]) * self.fromSpinBox.value()
KeyError: ''

Process finished with exit code 1