docs: def boundingBox(booleanArray):
      """
      return indices of the smallest bounding box enclosing all
      non-zero values within an array
  
      >>> a = np.array([ [0,0,0,0],
      ...                [0,1,0,1],
      ...                [0,0,1,0],
      ...                [1,0,0,0],
      ...                [0,0,0,0] ])
      >>> print ( boundingBox(a) ) 
      (slice(1, 3, None), slice(0, 3, None))
      """
  
      w = np.where(booleanArray)
      p = []
      for i in w:
          if len(i):
              p.append(slice(i.min(), i.max()))
          else:
              p.append(slice(0, 0))
  #             return None
      return tuple(p)