def __init__(self, worker_device, ps_devices):
        """
        Args:
            worker_device: the device to use for compute ops.
            ps_devices: a list of device to use for Variable ops.
        """
        self.ps_devices = ps_devices
        self.worker_device = worker_device
        self.ps_sizes = [0] * len(self.ps_devices)

        Args:
            worker_device: the device to use for compute ops.
            ps_devices: a list of device to use for Variable ops.
        
tensorpack/graph_builder/utils.py