When device_type is not provided, devices of the default type are
returned. This function nevers return a mix of device types, for instance
GPUs and CPUs.
Args
device_type
string, one of "cpu", "gpu" or "tpu". Defaults to
"gpu" or "tpu" if available when device_type is not provided.
Otherwise returns the "cpu" devices.
Return
List of string, the devices that are available for distributed
computation. Each device is formatted as "device_type:id", for instance
"gpu:1" or "cpu:0".