* 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

* gradients; test=document_fix

* fix VarType; test=document_fix

* fix vartype; test=document_fix

* cumsum; test=document_fix

* t; test=document_fix

* for test_mnist.py

* remove comments

* using type() replace isinstance()

* valid vars for run program OP in io.py

* open test_mnist in eager_gurad for coverage

add __all__=[] to python files not in API public list; import * only support in API public list files (#32643)

* add static check on data()

* follow comments

* fix ut

* add InputSpec

* add unittest for tensorSpec and SimpleNet

* add static data

* Rename `Input` into `InputSpec`

* fix argument place of Input api