def _validate_monkeys(self):
first_month = Monkey.unslash(self.ui.firstMonthEdit.text())
last_month = Monkey.unslash(self.ui.lastMonthEdit.text())
if not Monkey.is_valid_pair(first_month, last_month):
msg = 'Invalid time frame: invalid month or first month after last month!'
QMessageBox.critical(QMessageBox(), 'Input Error', msg)
self.ui.firstMonthEdit.setFocus()
return None
return TimeInterval(first_month=first_month, last_month=last_month)
