code: def alter_column(conn, table, column_name, func, schema=None):
      
      activity_table = get_activity_table(schema=schema)
      query = (
          activity_table
          .update()
          .values(
              old_data=(
                  activity_table.c.old_data +
                  sa.cast(sa.func.json_build_object(
                      column_name,
                      func(
                          activity_table.c.old_data[column_name],
                          activity_table
                      )
                  ), JSONB)
              ),
              changed_data=(
                  activity_table.c.changed_data +
                  sa.cast(sa.func.json_build_object(
                      column_name,
                      func(
                          activity_table.c.changed_data[column_name],
                          activity_table
                      )
                  ), JSONB)
              )
          )
          .where(activity_table.c.table_name == table)
      )
      return conn.execute(query)
docs: Run given callable against given table and given column in activity table
      jsonb data columns. This function is useful when you want to reflect type
      changes in your schema to activity table.
  
      In the following example we change the data type of User's age column from
      string to integer.
  
  
      ::
  
          from alembic import op
          from postgresql_audit import alter_column
  
  
          def upgrade():
              op.alter_column(
                  'user',
                  'age',
                  type_=sa.Integer
              )
  
              alter_column(
                  op,
                  'user',
                  'age',
                  lambda value, activity_table: sa.cast(value, sa.Integer)
              )
  
  
      :param conn:
          An object that is able to execute SQL (either SQLAlchemy Connection,
          Engine or Alembic Operations object)
      :param table:
          The table to run the column name changes against
      :param column_name:
          Name of the column to run callable against
      :param func:
          A callable to run against specific column in activity table jsonb data
          columns. The callable should take two parameters the jsonb value
          corresponding to given column_name and activity table object.
      :param schema:
          Optional name of schema to use.