code: def _shift(ix, periods):
      """Shift pandas index by periods."""
      if isinstance(
          ix, (pd.DatetimeIndex, pd.PeriodIndex, pd.TimedeltaIndex)
      ):
          return ix.shift(periods)
      else:
          return ix + periods
  
imports: from typing import Union
  import numpy
  import pandas
  from sklearn.utils import check_array
  from sktime.datatypes._utilities import get_cutoff, update_data
  from sktime.transformations.base import BaseTransformer
  from sktime.utils.validation import is_int
label_desc: Use image node_id 4 for calling a global function with example usage: _shift(ix, periods) and returns: ix, unknown