code: def to_timestamp(self, freq=None, how='start', copy=True):
          
          new_values = self._values
          if copy:
              new_values = new_values.copy()
  
          new_index = self.index.to_timestamp(freq=freq, how=how)
          return self._constructor(new_values,
                                   index=new_index).__finalize__(self)
docs: Cast to DatetimeIndex of Timestamps, at *beginning* of period.
  
          Parameters
          ----------
          freq : str, default frequency of PeriodIndex
              Desired frequency.
          how : {'s', 'e', 'start', 'end'}
              Convention for converting period to timestamp; start of period
              vs. end.
          copy : bool, default True
              Whether or not to return a copy.
  
          Returns
          -------
          Series with DatetimeIndex