class_docstr: Abstract base class for holding custom ``load``, ``invoke`` and ``prepare`` functions.
  
  Provides a skeleton for customization to override the methods
  ``load``, ``invoke`` and ``prepare``.
docstr: Custom prepare function
docstr_tok: ["Custom","prepare","function"]
code: def prepare(self, *args, **kwargs):
      """Custom prepare function"""
  
imports: from __future__ import absolute_import
  import abc
label_desc: Use image node_id 3 for calling the InferenceSpec obj's underlying member method code with example usage: obj.prepare() without return types