I just made this change for firmware-nonfree, for which I wrote:
We open some, but not all, files with an explicit UTF-8 encoding. One
of the open calls that I missed has just caused gencontrol.py to fail
instead a pbuilder environment. Instead of continuing to set an
explicit encoding for each open call, use locale.setlocale to set it
globally.
I haven't hit such a problem here, but let's do it anyway.
Keep using explicit encodings in debian/lib for now, since we can't
assume all calling programs will set the locale.
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