def acquire(self):
        """
        Locks the account. Returns True on success, False if the account
        is thread-local and must not be locked.
        """
        if self.host:
            self.parent.send(('acquire-account-for-host', self.host))
        elif self.account_hash:
            self.parent.send(('acquire-account-from-hash', self.account_hash))
        else:
            self.parent.send(('acquire-account'))

        response = self.parent.recv()
        if isinstance(response, Exception):
            raise response
        if response is None:
            return False

        self.account_hash, \
            self.user, \
            self.password, \
            self.authorization_password, \
            self.key = response
        return True
Locks the account. Returns True on success, False if the account
        is thread-local and must not be locked.