class_docstr: Calculate the population variance of a column.
  
  For the sample variance see :class:`.Variance`.
  
  :param column_name:
      The name of a column containing :class:`.Number` data.
class_docstr_tok: ["Calculate","the","population","variance","of","a","column",".","For","the","sample","variance","see",":","class",":","`",".Variance","`",".",":","param","column_name",":","The","name","of","a","column","containing",":","class",":","`",".Number","`","data","."]
code: def validate(self, table):
      column = table.columns[self._column_name]
  
      if not isinstance(column.data_type, Number):
          raise DataTypeError(
              "PopulationVariance can only be applied to columns containing Number data."
          )
  
      has_nulls = HasNulls(self._column_name).run(table)
  
      if has_nulls:
          warn_null_calculation(self, column)
  
file_path: agate/agate/aggregations/variance.py
imports: from agate.aggregations.base import Aggregation
  from agate.aggregations.has_nulls import HasNulls
  from agate.aggregations.mean import Mean
  from agate.data_types import Number
  from agate.exceptions import DataTypeError
  from agate.warns import warn_null_calculation
label_desc: Use image node_id 3 for calling the PopulationVariance obj's underlying member method code with example usage: obj.validate(table) without return types