Now that I understand that it's *types* that cause the problem with l…

…eading underscores, rename our private module back to private again.

setup.py

@@ -57,11 +57,9 @@ def cythonize(extensions, **_kwargs):
 # This list is derived from the profile of bm_simple_iface
 # https://github.com/NextThought/nti.externalization/commit/0bc4733aa8158acd0d23c14de2f9347fb698c040
 if not PYPY:
-    # Cython cannot properly handle double leading underscores, so
-    # our implementation modules can't start with an underscore.
     for mod_name in (
             'externalization',
-            'base_interfaces', # private
+            '_base_interfaces',
             'datastructures',
             'internalization',
             'singleton',

src/nti/externalization/base_interfaces.py → src/nti/externalization/_base_interfaces.py

@@ -69,4 +69,4 @@ def make_external_dict():
     return LocatedExternalDict()
 
 from nti.externalization._compat import import_c_accel # pylint:disable=wrong-import-position
-import_c_accel(globals(), 'nti.externalization._base_interfaces')
+import_c_accel(globals(), 'nti.externalization.__base_interfaces')

src/nti/externalization/_externalization.pxd

@@ -1,7 +1,7 @@
 # definitions for externalization.pxd
 import cython
 
-from ._base_interfaces cimport make_external_dict
+from .__base_interfaces cimport make_external_dict
 
 
 # Imports

src/nti/externalization/externalization.py

@@ -38,8 +38,8 @@
 from zope.security.interfaces import IPrincipal
 from zope.security.management import system_user
 
-from .base_interfaces import make_external_dict
-from .base_interfaces import NotGiven
+from ._base_interfaces import make_external_dict
+from ._base_interfaces import NotGiven
 
 
 from ._compat import identity