use locale.getpreferredencoding() to prevent OS X locale issues

[ntessore]

There is an issue on OS X when the locale is set to UTF-8 (no language), which happens out of the box on some systems. This has been reported before in #3870 and #5481. Such a locale cannot be parsed by Python's locale.getdefaultlocale(), which will throw

ValueError: unknown locale: UTF-8

when importing matplotlib.

Python issue 18378 deals with this matter. There you will find the suggestion that a project should use locale.getpreferredencoding() over locale.getdefaultlocale()[1], which coincidentally also fixes the issue on OS X. The PR implements this change.

[jenshnielsen]

Thanks that is probably the right way to go. I think we can set do_setlocale to false to make it safer see the python docs

[ntessore]

@jenshnielsen I wasn't sure about that flag, have put it in now.

[tacaswell]

Backported to 1.5.x as 2ac494f

[mangolzy]

with numpy 1.11.2 and update my matplotlib to 1.5.1, and the change of setting in ~/.bash_profile, I find no problem in bash shell.
But, the error still exist when I use ipython, could anybody kindly tell what should be set before I can successfully import matplotlib in Ipython? ( i can't understand this suggestion : a project should use locale.getpreferredencoding() over locale.getdefaultlocale()[1] since i don't use locale.getdefaultlocale()[1] at all...where to be replaced?)
thank you!

[jenshnielsen]

The change to local is within Matplotlib. This has been implemented in Matplotlib 1.5.2 so the easiest is to upgrade. It's also been fixed in OSX 10.12 as far as I know (this is really a bug in OSX) and a work around has been added to python to 2.7.12 and 3.5.2 as far as I know.