code: def get_column(column_name, node, context):
      
      column = try_get_column(column_name, node, context)
      if column is None:
          selectable = get_node_selectable(node, context)
          raise AssertionError(
              u'Column "{}" not found in selectable "{}". Columns present are {}. '
              u'Context is {}.'.format(column_name, selectable.original,
                                       [col.name for col in selectable.c], context))
      return column
docs: Get a column by name from the selectable.
  
      Args:
          column_name: str, name of the column to retrieve.
          node: SqlNode, the node the column is being retrieved for.
          context: CompilationContext, compilation specific metadata.
  
      Returns:
          column, the SQLAlchemy column if found. Raises an AssertionError otherwise.