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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 add(device_id, host, adbkey='', adb_server_ip='', adb_server_port=5037):
 """ Add a device. Creates FireTV instance associated with device identifier. :param device_id: Device identifier. :param host: Host in <address>:<port> format. :param adbkey: The path to the "adbkey" file :param adb_server_ip: the IP address for the ADB server :param adb_server_port: the port for the ADB server :returns: Added successfully or not. """

    valid = is_valid_device_id(device_id) and is_valid_host(host)
    if valid:
        devices[device_id] = FireTV(str(host), str(adbkey), str(adb_server_ip), str(adb_server_port))
    return valid