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here are changes that are not compatible in py2 and py3, i use six to keep compatibility

Changes

1. Data Mapping can't support different data type now

   Data Mapping use BTrees (like OLBTree from Zope/BTrees package) which use keys that must be comparable with <

   because they are internally stored in a sorted structure.

   but in py3, it raise error when compare between different types, for example, tuple and list

      TypeError: '<' not supported between instances of 'tuple' and 'list'

   i think it's hard to make it supported, so only update test for now

2. some method and script now use six to keep compatibility in py2&3