code: def unpatch_torch():
      """unpatch_torch is used to unpatch optimized torch classes to original ones."""
      global is_torch_patched
      if not is_torch_patched:
          return
  
      mapping_torch = _get_patch_map()
  
      for mapping_iter in mapping_torch:
          setattr(mapping_iter[0], mapping_iter[1], mapping_iter[3])
  
      unpatch_cuda()
  
      is_torch_patched = False
  
imports: import os
  from importlib.util import find_spec
  from bigdl.nano.pytorch.patching.gpu_cpu import patch_cuda, unpatch_cuda, get_cuda_status
label_desc: Use image node_id 3 for calling a global function with example usage: unpatch_torch() without return types