code: def var_str(shape):
      
  
      if shape in [None, ()]:
          return ['v1', ]
  
      size = np.prod(shape)
      indices = (np.indices(shape) + 1).reshape(-1, size)
      return ['v' + '_'.join(list(map(str, i))) for i in zip(*indices)]
docs: Return a sequence of strings naming the element of the tallyable object.
  
      :Examples:
      >>> var_str((5,))
      ['v1', 'v2', 'v3', 'v4', 'v5']
  
      >>> var_str((2,2))
      ['v1_1', 'v1_2', 'v2_1', 'v2_2']