code: def _reload(self, module=None):
          
          if self.module is None:
              raise RuntimeError
          elif module is None:
              import importlib
  
              module = ModuleSource(importlib.reload(module))
          elif module.name != self.module:
              raise RuntimeError
  
          if self.name in module.funcs:
              func = module.funcs[self.name]
              self.__init__(func=func)
          else:
              self.__init__(func=NULL_FORMULA)
  
          return self
docs: Reload the source function from the source module.
  
          **Internal use only**
          Update the source function of the formula.
          This method is used to updated the underlying formula
          when the source code of the module in which the source function
          is read from is modified.
  
          If the formula was not created from a module, an error is raised.
          If ``module_`` is not given, the source module of the formula is
          reloaded. If ``module_`` is given and matches the source module,
          then the module_ is used without being reloaded.
          If ``module_`` is given and does not match the source module of
          the formula, an error is raised.
  
          Args:
              module_: A ``ModuleSource`` object
  
          Returns:
              self