def __init__(self, devices=None):
        """
        Args:
            devices (list[int]): physical GPU ids to monitor. If None, will guess from the environment.
        """
        assert os.name != 'nt', "GPUUtilizationTracker does not support windows!"
        self._devices = devices
        self._enabled = True

        Args:
            devices (list[int]): physical GPU ids to monitor. If None, will guess from the environment.
        
tensorpack/callbacks/prof.py