* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* update

* fix bugs

* modify code style

* fix bugs of _get_global_group

* merge latest develop branch

* fix bugs

* update

* fix bugs for unittest

* modify for less use of gpu mem

* fix bugs of using _reset_grad_inplace_version

* update

* update

* modify for CI-Coverage

* retrick all CIs