class_docstr: Base layer class.
  
  Parameters
  ----------
  input_size : list
      size of the layer input
  output_size : list
      size of the layer output
  activation : str or None
      activation function name
  input_index_mapper : IndexMapper or None
      map indexes from this layer index to the input layer index size
code: def _eval(self, x):
      raise NotImplementedError()
  
imports: import itertools
  import numpy
label_desc: Use image node_id 12 for calling the Layer obj's underlying member method code with example usage: obj._eval(x) without return types