def spend_key(self):
        """
        Returns private spend key. None if wallet is view-only.

        :rtype: str or None
        """
        key = self._backend.spend_key()
        if key == numbers.EMPTY_KEY:
            return None
        return key
def spend_key(self):
        """
        Returns private spend key. None if wallet is view-only.

        :rtype: str or None
        """
        key = self._backend.spend_key()
        if key == numbers.EMPTY_KEY:
            return None
        return key
def spend_key ( self ) : key = self . _backend . spend_key ( ) if key == numbers . EMPTY_KEY : return None return key
Returns private spend key. None if wallet is view-only.

        :rtype: str or None
Returns private spend key . None if wallet is view - only .