code: def asfreq(obj, freq, method=None, how=None, normalize=False, fill_value=None):
      
      if isinstance(obj.index, PeriodIndex):
          if method is not None:
              raise NotImplementedError("'method' argument is not supported")
  
          if how is None:
              how = 'E'
  
          new_obj = obj.copy()
          new_obj.index = obj.index.asfreq(freq, how=how)
  
      elif len(obj.index) == 0:
          new_obj = obj.copy()
          new_obj.index = obj.index._shallow_copy(freq=to_offset(freq))
  
      else:
          dti = date_range(obj.index[0], obj.index[-1], freq=freq)
          dti.name = obj.index.name
          new_obj = obj.reindex(dti, method=method, fill_value=fill_value)
          if normalize:
              new_obj.index = new_obj.index.normalize()
  
      return new_obj
docs: Utility frequency conversion method for Series/DataFrame.