This module is a polyfill, implementing ChainMap for reasonably-recent versions of Python that do not have collections.ChainMap–namely, Python 2.6, Python 3.2, and PyPy3 releases based on Python 3.2. (It will also work as expected on Python 2.7, PyPy, and Python 3.3 and higher, but it is not needed there since those verions’ collections modules contains a ChainMap implementation.) The code for this package is closely derived from the Python 3.5 source code at hg.python.org, (especially the collections and reprlib modules). Several changes have been made to ensure Python 2.6 compatibility, and tests and packaging have been added.