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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def activation_key_expired(self):
 """ Checks if activation key is expired. Returns ``True`` when the ``activation_key`` of the user is expired and ``False`` if the key is still valid. The key is expired when it's set to the value defined in ``ACCOUNTS_ACTIVATED`` or ``activation_key_created`` is beyond the amount of days defined in ``ACCOUNTS_ACTIVATION_DAYS``. """

        expiration_days = datetime.timedelta(
                            days=defaults.ACCOUNTS_ACTIVATION_DAYS)
        expiration_date = self.date_joined + expiration_days
        if self.activation_key == defaults.ACCOUNTS_ACTIVATED:
            return True
        if get_datetime_now() >= expiration_date:
            return True
        return False