code: def _class_instance_from_name(class_name, *arg, **kwarg):
      
      # we first look in tc.extensions for the class name
      module_path = class_name.split('.')
      import_path = module_path[0:-1]
      module = __import__('.'.join(import_path), fromlist=[module_path[-1]])
      class_ = getattr(module, module_path[-1])
      instance = class_(*arg, **kwarg)
      return instance
docs: class_name is of the form modA.modB.modC.class module_path splits on "."
      and the import_path is then ['modA','modB','modC'] the __import__ call is
      really annoying but essentially it reads like:
  
      import class from modA.modB.modC
  
      - Then the module variable points to modC
      - Then you get the class from the module.