class_docstr: `ModelBase` is the base class of the `parl.Model` in different frameworks.
  
  This base class mainly do the following things:
      1. Implements APIs to manage model_id of the `parl.Model`; 
      2. Defines common APIs that `parl.Model` should implement in different frameworks.
docstr: Call forward function.
          
code: def __call__(self, *args, **kwargs):
      """Call forward function."""
      return self.forward(*args, **kwargs)
  
file_path: PARL/parl/core/model_base.py
label_desc: Use image node_id 7 for calling the ModelBase obj's underlying member method code with example usage: obj.__call__() and returns: self