ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__

[Marius Gedminas]

Importing lxml.etree produces an ImportWarning on Python 3.6. These warnings are suppressed by default, so to see them you have to set PYTHONWARNINGS=default.

Steps to reproduce:

    $ python3.6 -Wd
    Python 3.6.0+ (default, Dec 27 2016, 08:48:59)
    [GCC 6.2.0 20161005] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import lxml.etree
    .../lib/python3.6/importlib/_bootstrap.py:205: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
      return f(*args, **kwds)

Version information:

Python : sys.version_info(major=3, minor=6, micro=0, releaselevel='final', serial=0)
lxml.etree : (4, 1, 1, 0)
libxml used : (2, 9, 7)
libxml compiled : (2, 9, 7)
libxslt used : (1, 1, 32)
libxslt compiled : (1, 1, 32)

[Marius Gedminas (mgedmin)]

If I set PYTHONWARNINGS=error::ImportWarning, I can see a full traceback, which is:

  File "<stdin>", line 1, in <module>
  File "src/lxml/etree.pyx", line 93, in init lxml.etree
  File "src/lxml/_elementpath.py", line 56, in init lxml._elementpath

[Chris Jerdonek (chris-jerdonek)]

This is probably related to this Cython issue ("Spurious ImportWarnings on 3.6+"):
https://github.com/cython/cython/issues/1720

[Marius Gedminas (mgedmin)]

Summary of that Cython issue:

- it's a Cython bug where it's trying to emulate Python 2 style relative imports on Python 3
- it's fixed in master, but not in any released Cython yet
- you can work around it if you use `from __future__ import absolute_import` in your Cython modules
  and avoid explicit relative imports as well.
- an alternative fix is to make sure you compile the Cython module using language_level=3

[Chris Jerdonek (chris-jerdonek)]

Are there any workarounds for users of lxml aside from wrapping lxml imports in blocks like the following?

with warnings.catch_warnings():
    warnings.simplefilter('ignore', category=ImportWarning)
    import lxml.etree

[scoder (scoder)]

I added an "absolute_imports" future line to the files. Will be released when I get to it.