class_docstr: Calculate the quintiles of a column based on its percentiles.
  
  Quintiles will be equivalent to the 20th, 40th, 60th and 80th percentiles.
  
  "Zeroth" (min value) and "Fifth" (max value) quintiles are included for
  reference and intuitive indexing.
  
  See :class:`Percentiles` for implementation details.
  
  This aggregation can not be applied to a :class:`.TableSet`.
  
  :param column_name:
      The name of a column containing :class:`.Number` data.
code: def __init__(self, column_name):
      self._column_name = column_name
  
file_path: agate/agate/aggregations/quintiles.py
imports: from agate.aggregations.base import Aggregation
  from agate.aggregations.has_nulls import HasNulls
  from agate.aggregations.percentiles import Percentiles
  from agate.data_types import Number
  from agate.exceptions import DataTypeError
  from agate.utils import Quantiles
  from agate.warns import warn_null_calculation
label_desc: Use image node_id 1 to create a new Quintiles object from inherited base classes: Aggregation with example: obj = Quintiles(column_name)