This is strictly not a Python 2.7 change, but Python 2.7 backported the new .viewitems() from Python 3, and instead of changing .items() to .viewitems() and later having to change them all into .items() again in Python 3, I opted to just change all .iteritems() to .items() so the code will work both now and with Python 3. The slowdown with Python 2 is not significant, and with Python 3 it will again be fast.