> No, the use of the underscore in _ssl is per convention that C
> implementation part of stdlib modules are moved into modules that
> start with an underscore. This doesn't mean that the APIs in
> those modules are private, otherwise many C implementations we have
> in the stdlib would be private :-)

The non-private C-implemented modules are these:

$ cd /usr/lib64/python2.7/lib-dynload ; echo [^_]*.so
array.so audioop.so binascii.so bz2.so cmath.so cPickle.so crypt.so cStringIO.so datetime.so dbm.so fcntl.so future_builtins.so gdbm.so grp.so itertools.so linuxaudiodev.so math.so mmap.so nis.so operator.so ossaudiodev.so parser.so pyexpat.so readline.so resource.so select.so spwd.so strop.so syslog.so termios.so time.so unicodedata.so zlib.so

_[^_]-prefixed, undocumented modules (amongst whom are both _[^_].py and _[^_].so) should be treated as private modules for usage only by public modules in standard library.

(_winreg is the only _[^_]-prefixed, documented module in CPython 2.7.)