The extras module contains additional features that are useful, but not part of the core puzzlepiece functionality. Currently this is just the datagrid - a Widget that can be added to your Pieces, with multiple Piece-like Rows that use params for data storage and manipulation.
The extras modules have to be imported explicitly:
# This will import the datagrid module:
from puzzlepiece.extras import datagrid
# The following will not work:
import puzzlepiece.extras as extras
extras.datagridpuzzlepiece.extras.datagrid