def send_invitation(self, user, sender=None, **kwargs):
        """An intermediary function for sending an invitation email that
        selects the templates, generating the token, and ensuring that the user
        has not already joined the site.
        """
        if user.is_active:
            return False
        token = self.get_token(user)
        kwargs.update({"token": token})
        self.email_message(
            user, self.invitation_subject, self.invitation_body, sender, **kwargs
        ).send()
        return True
An intermediary function for sending an invitation email that
        selects the templates, generating the token, and ensuring that the user
        has not already joined the site.