code: def list_physical_devices(device_type=None):
      """Return a list of physical devices visible to the host runtime.
  
      Physical devices are hardware devices present on the host machine. By default
      all discovered CPU and GPU devices are considered visible.
  
      This API allows querying the physical hardware resources prior to runtime
      initialization. Thus, giving an opportunity to call any additional
      configuration APIs. This is in contrast to `tf.config.list_logical_devices`,
      which triggers runtime initialization in order to list the configured devices.
  
      The following example lists the number of visible GPUs on the host.
  
      >>> physical_devices = tf.config.list_physical_devices('GPU')
      >>> print("Num GPUs:", len(physical_devices))
      Num GPUs: ...
  
      However, the number of GPUs available to the runtime may change during runtime
      initialization due to marking certain devices as not visible or configuring
      multiple logical devices.
  
      Args:
        device_type: (optional string) Only include devices matching this device
          type. For example "CPU" or "GPU".
        Notes: 1. If provided with any numerical values or any string other than
          supported device type such as 'CPU' it returns an empty list instead of
          raising error. 2. For default value it returns all physical devices
  
      Returns:
        List of discovered `tf.config.PhysicalDevice` objects
      """
      return context.context().list_physical_devices(device_type)
  
imports: from typing import Union
  from tensorflow.python.eager import context
  from tensorflow.python.framework import errors
  from tensorflow.python.util import _pywrap_determinism
  from tensorflow.python.util import _pywrap_tensor_float_32_execution
  from tensorflow.python.util import deprecation
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 17 for calling a global function with example usage: list_physical_devices(device_type) and returns: context