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Python2 to Python3 conversion

Python2 to Python3 migration for CMS DMWM stack

Description: CMS collaboration is looking for a student to complete ongoing effort to migrate DMWM (Data Management and Workflow Management) stack from python2 to python3. The DMWM stack consists of about 200K lines of code along with about 100 external python packages. A qualified candidate will involve of setting up VM, build python externals in python3, convert DMWM code and perform numerious tests among two version of python. Required skills Python language, Linux, UNIX tools Tags: python, unix scripts

The goal is py2/py3 transition to produce valid py2/py3 code that moves us towards running on py3

Read twiki [1] about futurize and this PR [2]
Setup CERN VM either using cmsweb setup [3] or docker [4]
Install futurize package (if necessary, should be already in docker setup)
Clone WMCore code, make new branch and applied futurize --stage2 to it here we'll break futurize by features, i.e. apply one feature at a time [5]
- exclude certain constructs from migration iteritems, ... # we need to provide full list This can be done manually or via changes to futurize package itself.
- document each feature changes on twiki, the documentation should come with simple example of py2 vs py3 styles, e.g.
  
  python2
  
  rdict = {} for key, val in rdict.iteritems():
  
  python3
  
  rdict = {} for key, val in rdict.items():
Run Unit tests via Jenkins [6], the PR will trigger Jenkins tests. If Jenkins unit tests fails we may rerun failed tests in a docker container [4]