* Add bf16 support for save and load ops

* Add bf16 test condition

* Add matmul and chagne fluid.io to paddle.static

* Reduce the test duration

* add atan2_op

* fix

* support non-tensor type

* fix unittest failed

* add unittest with prune

* rm unused code

* coverage

* fix two or

* Add lookup_table_v2 BF16

* Reuse lookup table UT

* Change op_type to op_version

* Remove check_dygraph

* Remove skip_check_grad_ci

* - Draft of implementation of refactoring

- compilation fix

* - Fixes after review

* - Removed unnecessary comment

* new api trunc, test=develop

* fix output padding conv

* add repr unittest for conv

* add return when input is tensor

* fix typo

* add pplayer

* add sharedlayerdesc

* use SparseSoftmaxCrossEntropyWithLogits

* fix

* test_slice

* revert test_slice

* add backprob for npu kernel

* fix typo

* fix ut

* fix ut

* refine comments

* return softmax

* Save all the information of 'ParamBase' in 'Layer'.

* edit unittest

add the support for the bool in compare ops

* add reduce_sum_op by add self-kernel

* set all ReduceKernel MPType for accuracy

* add float16 test script which input is integer number

* solve reduce sum float16 check_grad problem

* solve conflict and change test script for CI

* change kernel register for CI

* remove all useless template

* Add digamma_op and unittest

* add digamma_op api

* remove special DigammaCudaKernel and correct some docs

* remove unused headers

* fix api doc error

This reverts commit b2afc8df.

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

* Eliminate numerical differences of LayerNorm; fix LayerNorm Nan Bug while large data input

* fix bug while large shape of data input

* add support for trt dynamic shape flatten op

* add version restriction

* add ut input dynamic shape

* Small changes related to BF16 fusion_gru and fusion_lstm

* Correct to pass arg by value

* Add conditions to rnn op

* Correct the spelling mistake

* Improving the test with checking activation

* Trigger CI

* fix gather shape bug

* fix None

* fix topo

* update spawn doc for xpu, test=ducument_fix

* add note for gpu and xpu, test=document_fix

* use PYTHON_C_API in dygraph, test=develop

* update 2.0 public api in all left files

* reverse device.py all list;
fix some flake8 errors

* update 2.0 public api in vision

* fix some flake8 errors

For python, if users write `a, b = var`, the `__getitem__` method will iterate through 0, 1, 2 ... until `__getitem__` throws an IndexError, then stop. The var[0], var[1] will be given to a, b respectively. If more values are given, the unpack size would cause error.

We didn't raise the IndexError in the past and we add statement in `__getitem__` to raise IndexError here to support grammar like `a, b = var` in this PR.