I patched readline (r81918) and locale (r81914) modules to use PyUnicode_FSConverter(). They don't use "z" format anymore to parse a filename.

I checked last functions using "z" format (not "z#" or "z*", only "z") and I think that it's ok ("z" can be patched to reject bytes). You can get the full list using:

grep -n 'PyArg_Parse[^(]*([^"]*"[^";:]*z[^#*]' */*.c

--

About the difference between s/z and s*/s#/z*/z#: I don't understand why they are different, but I think that it's too late to change that. Too much functions (and third party modules?) suppose that s*/s#/z*/z# supports buffer compatible objects.