code: def depth_slice(self):
          
  
          if self.depth is not None:
              return self.depth
  
          from .depth import Depth
          self.depth = Depth(self)
          return self.depth
docs: Interact with segy in depth slice mode (fixed z-coordinate)
  
          Returns
          -------
          depth : Depth
  
          Notes
          -----
          .. versionadded:: 1.1
  
          .. versionchanged:: 1.7.1
              enabled for unstructured files