class_docstr: Base parameter fitting estimator class.
  
  The base parameter fitter specifies the methods and method signatures that all
  parameter fitter have to implement.
  
  Specific implementations of these methods is deferred to concrete instances.
docstr: Update fitted parameters on more data.
  
  private _update containing the core logic, called from update
  
  State required:
      Requires state to be "fitted".
  
  Accesses in self:
      Fitted model attributes ending in "_"
  
  Writes to self:
      Sets fitted model attributes ending in "_"
  
  Parameters
  ----------
  X : guaranteed to be of a type in self.get_tag("X_inner_mtype")
      Time series with which to update the estimator.
  
  Returns
  -------
  self : reference to self
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code: def _update(self, X):
      """Update fitted parameters on more data.
  
      private _update containing the core logic, called from update
  
      State required:
          Requires state to be "fitted".
  
      Accesses in self:
          Fitted model attributes ending in "_"
  
      Writes to self:
          Sets fitted model attributes ending in "_"
  
      Parameters
      ----------
      X : guaranteed to be of a type in self.get_tag("X_inner_mtype")
          Time series with which to update the estimator.
  
      Returns
      -------
      self : reference to self
      """
      # default to re-fitting if update is not implemented
      warn(
          f"NotImplementedWarning: {self.__class__.__name__} "
          f"does not have a custom `update` method implemented. "
          f"{self.__class__.__name__} will be refit each time "
          f"`update` is called.",
          obj=self,
      )
      # refit with updated data, not only passed data
      self.fit(X=self._X)
      # todo: should probably be self._fit, not self.fit
      # but looping to self.fit for now to avoid interface break
  
      return self
  
file_path: sktime/sktime/param_est/base.py
imports: from sktime.base import BaseEstimator
  from sktime.datatypes import VectorizedDF, check_is_scitype, convert, scitype_to_mtype, update_data
  from sktime.utils.sklearn import is_sklearn_transformer
  from sktime.utils.validation._dependencies import _check_estimator_deps
  from sktime.utils.warnings import warn
label_desc: Use image node_id 8 for calling the BaseParamFitter obj's underlying member method code with example usage: obj._update(X) and returns: self