docstr: Copy which contains ``count`` future timestamps.
  
  >>> p = periods("2021", "D", 365)
  >>> assert p.extend(5) == periods("2021", "D", 370)
code: def extend(self, count: int) -> Periods:
      """
      Copy which contains ``count`` future timestamps.
  
      >>> p = periods("2021", "D", 365)
      >>> assert p.extend(5) == periods("2021", "D", 370)
  
      """
      return Periods(
          np.concatenate([self.data, self.future(count).data]),
          self.freq,
      )
  
imports: from __future__ import annotations
  import datetime
  import functools
  from dataclasses import dataclass
  from typing import Any, Union, Optional, Tuple, cast, overload
  import numpy
  from dateutil.parser import parse
  from gluonts.core import serde
  from ._freq import Freq
label_desc: Use image node_id 8 for calling the Periods obj's underlying member method code with example usage: obj.extend(count) and returns: Periods