add get_rule_for_parents and add docs for set_rule_for_parents
tests for get_rule_for_parents and revised tests for _update_rule_for_parents
improve _set_rule_for_parents function
add tests for set_rule_for_parents
Change get_parents function
Add tests for get_parents function
made _get_parent_objects function one liner
tests for _get_parent_objects
pep8 fix
Merge pull request #50 from ankurankan/dev

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