bpo-31107: Fix copyreg mangled slot names calculation.

Lib/copyreg.py

@@ -128,7 +128,11 @@ class found there. (This assumes classes don't modify their
  continue
  # mangled names
  elif name.startswith('__') and not name.endswith('__'):
- names.append('_%s%s' % (c.__name__, name))
+ stripped = c.__name__.lstrip('_')
+ if stripped:
+ names.append('_%s%s' % (stripped, name))
+ else:
+ names.append(name)
  else:
  names.append(name)
 

Lib/test/test_copyreg.py

@@ -16,6 +16,12 @@ class WithWeakref(object):
 class WithPrivate(object):
  __slots__ = ('__spam',)
 
+class _WithLeadingUnderscoreAndPrivate(object):
+ __slots__ = ('__spam',)
+
+class ___(object):
+ __slots__ = ('__spam',)
+
 class WithSingleString(object):
  __slots__ = 'spam'
 
@@ -104,6 +110,10 @@ def test_slotnames(self):
  self.assertEqual(copyreg._slotnames(WithWeakref), [])
  expected = ['_WithPrivate__spam']
  self.assertEqual(copyreg._slotnames(WithPrivate), expected)
+ expected = ['_WithLeadingUnderscoreAndPrivate__spam']
+ self.assertEqual(copyreg._slotnames(_WithLeadingUnderscoreAndPrivate),
+ expected)
+ self.assertEqual(copyreg._slotnames(___), ['__spam'])
  self.assertEqual(copyreg._slotnames(WithSingleString), ['spam'])
  expected = ['eggs', 'spam']
  expected.sort()

Misc/NEWS.d/next/Library/2017-08-02-12-48-15.bpo-31107.1t2hn5.rst

@@ -0,0 +1,2 @@
+Fix `copyreg._slotnames()` mangled attribute calculation for classes whose
+name begins with an underscore. Patch by Shane Harvey.