* del python2 code

* cherry-pick 33556

cherry-pick Specify gast version in requirements.txt

* [2.0.1]Support New Custom OP on windows

* fix CI

* fix code style

* fix CI

* fix CI

* fix coverage

* fix CI

* fix CI

gast version can be conflict with the other software users installed. We set the version to be higher than 0.3.3

* lazy import for scipy

* rm unused check

* test=develop, rm pathlib

Remove NLTK requirements to avoid dependency security alert from Github Dependabot

* test=develop, rm netifaces

* rm dependence of cv2

* remove objgraph

* remove graphviz

* fix ut

set default python3,fix incompatible,cache dir for third party,unify error code,for windows (#26178)

* set default python3 for paddle windows,test=win

* set default python3,cache dir for third party,error code,test=win

* fix some incompatible

* fix some error

* set virtual environment,test=win

* test=develop,test=document_fix, remove the out args

* fleet_util move to paddle.fleet
Co-authored-by: NWuHaobo <wuhaobo1994@gmail.com>
Co-authored-by: Ntangwei12 <tangwei12@baidu.com>

* support nested if/else

* support to derivate returns the parameter list automatically

* polish tranform function of slice

* fix modify x.numpy()[i] slice function

* support to transform ast.node into callable function

* fix get_name_ids bug and add more unittest test=develop

* fix requirements.txt test=develop

* remove useless import statement test=develop

* Fixed version compatibility issues in param of function test=develop

* use decorater to test ast_to_func test=develop

* add textwrap.dedent for source_code test=develop

* polish code comment

* fix compatibility with python2 and python3 test=develop

* fix gast version error test=develop

* fix gast repo test=develop

* polish transfer_from_node_type code test=develop

* add nested_if_else unittest test=develop

* split IfElseTransformer test=develop

* specify gast version test=develop

* fix ast_to_func root type test=develop

1. Move AstNodeWrapper, StaticAnalysisVisitor to a new python file: static_analysis.py
2. Add basic node var type analysis

* add xly py35 dockerfile

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test dockerfile

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35

* test=py35,test=develop,test=inference,test=document_fix

* refactor dygraph,test=develop

* fix failed unittest,test=develop

* polish code,test=develop

* check windows ci error,test=develop
try to fix windows ci error by np.allclose,test=develop

* polish vlog and profiler, test=develop

* try to fix preceding ops order,test=develop

* test transformer in windows ci, test=develop

* use python c-api to speed up tracer.trace,test=develop

* test=develop, fix docker with paddle nccl problem

* test=develop, add ut for debug string and gradient_accumulator

* test=develop, add tests for layer/gradient_accumulator/prepared_op

* test=develop, fix complie error for test_prepared_op

* test=develop, add more ut for dygraph

* test=develop, create API.spec for dygraph api change

* test=develop, refoctor name to make it easier to understand

* test=develop, refoctor name to make it easier to understand

* test=develop, fix multi-gpu failed problem , add Tracer tests, change PADDLEENFORCE to PADDLEENFORCE_EQ

* test=develop, fix ut failed on parallel se-resnext

* test=develop, change one more PADDLE_ENFORCE

As mentioned in this link, the last version of NumPy to support Python 2.7 is numpy 1.16.4.

remove pycpuinfo deps in core

* fix mac ci random fail
* use platform instead

* fix py-cpuinfo mac random fail
* differentiate version on windows

test=develop

update config for matplotlib, because python 3.6 is required by 3.1+