class_docstr: Calculate the sum of a column.
  
  :param column_name:
      The name of a column containing :class:`.Number` data.
code: def run(self, table):
      column = table.columns[self._column_name]
  
      start = 0
      if isinstance(column.data_type, TimeDelta):
          start = datetime.timedelta()
  
      return sum(column.values_without_nulls(), start)
  
file_path: agate/agate/aggregations/sum.py
imports: import datetime
  from agate.aggregations.base import Aggregation
  from agate.data_types import Number, TimeDelta
  from agate.exceptions import DataTypeError
label_desc: Use image node_id 4 for calling the Sum obj's underlying member method code with example usage: obj.run(table) and returns: sum