* [CodeStyle] remove all future import

* revert test_error.py

* restore future import in example code

* 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

* eager math op, test=develop

* eager support lookahead, test=develop

* refine,test=develop

* refine doc, test=develop

* refine,test =develop

* refie, test=develop

* refie, test=develop

* refie, test=develop

* test_paddle_multiprocessing

* refine, test=develop

* refine, test=develop

* fix bug, test=develop

* refine, test=develop

* dataloader, test=develop

* refine, test=develop

* refine, test=develop

* refine, test=develop

* test_datasets timeout, test=develop

* refine, test=develop

* fix drop_last not work in IterableDataset. test=develop

* add warning log for DataLoader output format imcompatible upgrade. test=develop

* add random state generate in DataLoader worker. test=develop

* add dict/str/list supprot for DataLoader. test=develop

* fix dataloader collate return list mix tensor and numpy array. test=develop

As the title 

* fix failed tests in yingchun gived list

* add unittests into static_mode_white_list

* add enable static

* fix dist unittest

* skip test_sigmoid_focal_loss_op & add gym

* revert no need skip unittests

* remove gym

* add paddle.io.ComposeDataset & paddle.io.ChainDataset. test=develop

* add TensorDataset. test=develop