code: def add_internal_var(self, internal_var):
      if not isinstance(internal_var, InternalVar):
          raise ValueError(
              "Only InternalVar can be manually added to Block."
          )
      self._internal_vars.add(internal_var)
  
imports: from collections import Counter, OrderedDict
  import copy
  import logging
  import numpy
  from six import string_types
  from .None import SPACES, types
  from .var import Var, InternalVar, ListVar
  from .visitors.dot_visitor import DotVisitor
  from .types.symbolic import k_used_symbols, k_num_internal_syms, any_symbolic, is_symbolic
  from .input_type import TupleInputType
label_desc: Use image node_id 6 for calling the Block obj's underlying member method code with example usage: obj.add_internal_var(internal_var) without return types