class_docstr: Calculate the interquartile range of a column.
  
  :param column_name:
      The name of a column containing :class:`.Number` data.
code: def run(self, table):
      percentiles = self._percentiles.run(table)
  
      if percentiles[75] is not None and percentiles[25] is not None:
          return percentiles[75] - percentiles[25]
  
file_path: agate/agate/aggregations/iqr.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.warns import warn_null_calculation
label_desc: Use image node_id 4 for calling the IQR obj's underlying member method code with example usage: obj.run(table) and returns: unknown