code: def add_hook(self, pc, callback):
          
          if not (isinstance(pc, int) or pc is None):
              raise TypeError(f"pc must be either an int or None, not {pc.__class__.__name__}")
          else:
              self._hooks.setdefault(pc, set()).add(callback)
              if self._hooks:
                  self._executor.subscribe('will_execute_instruction', self._hook_callback)
docs: Add a callback to be invoked on executing a program counter. Pass `None`
          for pc to invoke callback on every instruction. `callback` should be a callable
          that takes one :class:`~manticore.core.state.State` argument.
  
          :param pc: Address of instruction to hook
          :type pc: int or None
          :param callable callback: Hook function