I've investigated a bit more.
First, I've tried with Python 3.7.0a1 . As you'd expect, PEP 537 means
this behaviour now also occurs when no locale environment variables at
all are set.
Second, I've looked through locale.py a bit. I believe what it calls the
"aliasing engine" is applied for:
- getlocale()
- getdefaultlocale()
- setlocale() when passed a tuple, but not when passed a string
This leads to some rather odd results.
With 3.7.0a1 and no locale environment variables:
>>> import locale
>>> locale.getlocale()
('en_US', 'UTF-8')
# getlocale() is lying: the effective locale is really C.UTF-8
>>> sorted("abcABC", key=locale.strxfrm)
['A', 'B', 'C', 'a', 'b', 'c']
Third, I've checked on a system which does have en_US.UTF-8 installed,
and (as you'd expect) instead of crashing it gives wrong results:
>>> import locale
>>> locale.setlocale(locale.LC_ALL, ('C', 'UTF-8'))
'en_US.UTF-8'
>>> locale.getlocale()
('en_US', 'UTF-8')
# now getlocale() is telling the truth, and the user isn't getting the
# collation they requested
>>> sorted("abcABC", key=locale.strxfrm)
['a', 'A', 'b', 'B', 'c', 'C']