def METHOD_NAME(
    self, vpn_gateway_id: str, vpc_id: str
) -> VPCGatewayAttachment:
    vpn_gateway = self.get_vpn_gateway(vpn_gateway_id)
    self.get_vpc(vpc_id)  # type: ignore[attr-defined]
    attachment = VPCGatewayAttachment(vpc_id, state="attached")
    for key in vpn_gateway.attachments.copy():
        if key.startswith("vpc-"):
            vpn_gateway.attachments.pop(key)
    vpn_gateway.attachments[vpc_id] = attachment
    return attachment