pyximport of .py files should use language_level=3 in Python 3

[robertwb]

When running under Python 3, any .py file that pyximport is triggered for can be expected to be in Python 3 syntax. Currently, pyximporting simply fails because of syntax errors because it does not configure the language level at all. Therefore, pyximport's import hook should automatically switch to -3 mode under Python 3 when compiling a .py file.

Note that the same is not true for .pyx files, which may or may not in Py3 syntax. So there should additionally be a way to configure the language level explicitly when installing the pyximport import hooks.

Migrated from http://trac.cython.org/ticket/733

[scoder]

This was already implemented in Cython 0.17 (8133605).

[hermidalc]

Unless I'm doing something wrong, as of 0.29.7 this is still not implemented at least when using pyximport. If you do not specify the language_level manually it gives you the FutureWarning: Cython directive 'language_level' not set, using 2 for now (Py2). This will change in a later release! even though it should know it's using Python 3.x.

[scoder]

@hermidalc are you sure you are referring to .py files? The automatic setting does not apply to .pyx files.

cython/pyximport/pyximport.py

Lines 346 to 347 in 19656b2

	if language_level is None:
	language_level = sys.version_info[0]

[hermidalc]

@hermidalc are you sure you are referring to .py files? The automatic setting does not apply to .pyx files.

cython/pyximport/pyximport.py

Lines 346 to 347 in 19656b2

	if language_level is None:
	language_level = sys.version_info[0]

Ok, sorry didn't know that.