Returns the history from cache or DB or a newly created one.

def get_history(self):
        """Returns the history from cache or DB or a newly created one."""
        if hasattr(self, '_history'):
            return self._history
        try:
            self._history = APICallDayHistory.objects.get(
                user=self.user, creation_date=now().date())
        except APICallDayHistory.DoesNotExist:
            self._history = APICallDayHistory(user=self.user)
            self._history.amount_api_calls = 0
        return self._history