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 run(self, table):
      column = table.columns[self._column_name]
  
      data = column.values_without_nulls()
      if data:
          mean = self._mean.run(table)
          return sum((n - mean) ** 2 for n in data) / len(data)
  
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 4 for calling the PopulationVariance obj's underlying member method code with example usage: obj.run(table) and returns: unknown