[code-quality] pylint3 ImportError when using PEP 420 namespaces

[Stefano Zacchiroli]

Heya,
  I'm trying to use pylint3 on a bunch of Python 3 modules that use PEP
420 implicit namespaces. All imports work just fine outside of pylint,
but most of them fail with an ImportError within pylint and I don't
understand why.

My understanding from the issue tracker was that this issue should've
been solved in the version of pylint I'm using. So either it's not, or
I'm missing something :)

A sample of the issues I'm facing is reported below.
Advice welcome!

  zack at scaramouche:~$ pylint3 --version
  pylint3 1.7.2, 
  astroid 1.5.3
  Python 3.5.4 (default, Aug 12 2017, 14:08:14) 
  [GCC 7.1.0]

  zack at scaramouche:~/swh/git/swh-environment/swh-model$ ls swh/model/
  exceptions.py  fields  git.py  hashutil.py  identifiers.py  __init__.py  __pycache__  tests  validators.py
  zack at scaramouche:~/swh/git/swh-environment/swh-model$ ls -l swh/model/__init__.py 
  -rw-r--r-- 1 zack zack 0 ago 29 12:53 swh/model/__init__.py
  zack at scaramouche:~/swh/git/swh-environment/swh-model$ python3
  Python 3.5.4 (default, Aug 12 2017, 14:08:14) 
  [GCC 7.1.0] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import swh.model
  >>> import swh.model.git
  >>> import swh.model.hashutil
  >>> 

So all works well with "pure" python3. Now let's see with pylint3:

  zack at scaramouche:~/swh/git/swh-environment/swh-model$ pylint3 swh.model.hashutil > /dev/null
  zack at scaramouche:~/swh/git/swh-environment/swh-model$ pylint3 swh.model.git > /dev/null

The above ones work, when loading leaf modules.

Loading the upper module "swh.model" doesn't work though:

  zack at scaramouche:~/swh/git/swh-environment/swh-model$ pylint3 swh.model > /dev/null
  Traceback (most recent call last):
    File "/home/zack/bin/pylint3", line 11, in <module>
      sys.exit(run_pylint())
    File "/home/zack/.local/lib/python3.5/site-packages/pylint/__init__.py", line 13, in run_pylint
      Run(sys.argv[1:])
    File "/home/zack/.local/lib/python3.5/site-packages/pylint/lint.py", line 1300, in __init__
      linter.check(args)
    File "/home/zack/.local/lib/python3.5/site-packages/pylint/lint.py", line 726, in check
      self._do_check(files_or_modules)
    File "/home/zack/.local/lib/python3.5/site-packages/pylint/lint.py", line 837, in _do_check
      for descr in self.expand_files(files_or_modules):
    File "/home/zack/.local/lib/python3.5/site-packages/pylint/lint.py", line 869, in expand_files
      self.config.black_list_re)
    File "/home/zack/.local/lib/python3.5/site-packages/pylint/utils.py", line 894, in expand_modules
      modpath = _modpath_from_file(subfilepath, is_namespace)
    File "/home/zack/.local/lib/python3.5/site-packages/pylint/utils.py", line 833, in _modpath_from_file
      return modutils.modpath_from_file_with_callback(filename, is_package_cb=_is_package_cb)
    File "/home/zack/.local/lib/python3.5/site-packages/astroid/modutils.py", line 310, in modpath_from_file_with_callback
      filename, ', \n'.join(sys.path)))
  ImportError: Unable to find module for /home/zack/dati/projects/sw-heritage/git/swh-environment/swh-model/swh/model/hashutil.py in /home/zack/dati/projects/sw-heritage/git/swh-environment/swh-model, 
  ., 
  /home/zack/.local/bin, 
  /home/zack/dati/projects/sw-heritage/git/swh-environment/swh-archiver, 

  [ long list of PYTHONPATH entries snipped ]

Any idea?

Cheers.
-- 
Stefano Zacchiroli . zack at upsilon.cc . upsilon.cc/zack . . o . . . o . o
Computer Science Professor . CTO Software Heritage . . . . . o . . . o o
Former Debian Project Leader & OSI Board Director  . . . o o o . . . o .
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