Issue #18473: Fixed 2to3 and 3to2 compatible pickle mappings.

Fixed ambigious reverse mappings.  Added many new mappings.  Import mapping
is no longer applied to modules already mapped with full name mapping.

Added tests for compatible pickling and unpickling and for consistency of
_compat_pickle mappings.

Lib/test/test_pickle.py

@@ -1,3 +1,6 @@
+from _compat_pickle import (IMPORT_MAPPING, REVERSE_IMPORT_MAPPING,
+                            NAME_MAPPING, REVERSE_NAME_MAPPING)
+import builtins
 import pickle
 import io
 import collections
@@ -207,9 +210,156 @@ if has_c_implementation:
             check(u, stdsize + 32 * P + 2 + 1)
 
 
+ALT_IMPORT_MAPPING = {
+    ('_elementtree', 'xml.etree.ElementTree'),
+    ('cPickle', 'pickle'),
+}
+
+ALT_NAME_MAPPING = {
+    ('__builtin__', 'basestring', 'builtins', 'str'),
+    ('exceptions', 'StandardError', 'builtins', 'Exception'),
+    ('UserDict', 'UserDict', 'collections', 'UserDict'),
+    ('socket', '_socketobject', 'socket', 'SocketType'),
+}
+
+def mapping(module, name):
+    if (module, name) in NAME_MAPPING:
+        module, name = NAME_MAPPING[(module, name)]
+    elif module in IMPORT_MAPPING:
+        module = IMPORT_MAPPING[module]
+    return module, name
+
+def reverse_mapping(module, name):
+    if (module, name) in REVERSE_NAME_MAPPING:
+        module, name = REVERSE_NAME_MAPPING[(module, name)]
+    elif module in REVERSE_IMPORT_MAPPING:
+        module = REVERSE_IMPORT_MAPPING[module]
+    return module, name
+
+def getmodule(module):
+    try:
+        return sys.modules[module]
+    except KeyError:
+        __import__(module)
+        return sys.modules[module]
+
+def getattribute(module, name):
+    obj = getmodule(module)
+    for n in name.split('.'):
+        obj = getattr(obj, n)
+    return obj
+
+def get_exceptions(mod):
+    for name in dir(mod):
+        attr = getattr(mod, name)
+        if isinstance(attr, type) and issubclass(attr, BaseException):
+            yield name, attr
+
+class CompatPickleTests(unittest.TestCase):
+    def test_import(self):
+        modules = set(IMPORT_MAPPING.values())
+        modules |= set(REVERSE_IMPORT_MAPPING)
+        modules |= {module for module, name in REVERSE_NAME_MAPPING}
+        modules |= {module for module, name in NAME_MAPPING.values()}
+        for module in modules:
+            try:
+                getmodule(module)
+            except ImportError as exc:
+                if support.verbose:
+                    print(exc)
+
+    def test_import_mapping(self):
+        for module3, module2 in REVERSE_IMPORT_MAPPING.items():
+            with self.subTest((module3, module2)):
+                try:
+                    getmodule(module3)
+                except ImportError as exc:
+                    if support.verbose:
+                        print(exc)
+                if module3[:1] != '_':
+                    self.assertIn(module2, IMPORT_MAPPING)
+                    self.assertEqual(IMPORT_MAPPING[module2], module3)
+
+    def test_name_mapping(self):
+        for (module3, name3), (module2, name2) in REVERSE_NAME_MAPPING.items():
+            with self.subTest(((module3, name3), (module2, name2))):
+                attr = getattribute(module3, name3)
+                if (module2, name2) == ('exceptions', 'OSError'):
+                    self.assertTrue(issubclass(attr, OSError))
+                else:
+                    module, name = mapping(module2, name2)
+                    if module3[:1] != '_':
+                        self.assertEqual((module, name), (module3, name3))
+                    self.assertEqual(getattribute(module, name), attr)
+
+    def test_reverse_import_mapping(self):
+        for module2, module3 in IMPORT_MAPPING.items():
+            with self.subTest((module2, module3)):
+                try:
+                    getmodule(module3)
+                except ImportError as exc:
+                    if support.verbose:
+                        print(exc)
+                if ((module2, module3) not in ALT_IMPORT_MAPPING and
+                    REVERSE_IMPORT_MAPPING.get(module3, None) != module2):
+                    for (m3, n3), (m2, n2) in REVERSE_NAME_MAPPING.items():
+                        if (module3, module2) == (m3, m2):
+                            break
+                    else:
+                        self.fail('No reverse mapping from %r to %r' %
+                                  (module3, module2))
+                module = REVERSE_IMPORT_MAPPING.get(module3, module3)
+                module = IMPORT_MAPPING.get(module, module)
+                self.assertEqual(module, module3)
+
+    def test_reverse_name_mapping(self):
+        for (module2, name2), (module3, name3) in NAME_MAPPING.items():
+            with self.subTest(((module2, name2), (module3, name3))):
+                attr = getattribute(module3, name3)
+                module, name = reverse_mapping(module3, name3)
+                if (module2, name2, module3, name3) not in ALT_NAME_MAPPING:
+                    self.assertEqual((module, name), (module2, name2))
+                module, name = mapping(module, name)
+                self.assertEqual((module, name), (module3, name3))
+
+    def test_exceptions(self):
+        self.assertEqual(mapping('exceptions', 'StandardError'),
+                         ('builtins', 'Exception'))
+        self.assertEqual(mapping('exceptions', 'Exception'),
+                         ('builtins', 'Exception'))
+        self.assertEqual(reverse_mapping('builtins', 'Exception'),
+                         ('exceptions', 'Exception'))
+        self.assertEqual(mapping('exceptions', 'OSError'),
+                         ('builtins', 'OSError'))
+        self.assertEqual(reverse_mapping('builtins', 'OSError'),
+                         ('exceptions', 'OSError'))
+
+        for name, exc in get_exceptions(builtins):
+            with self.subTest(name):
+                if exc in (BlockingIOError, ResourceWarning):
+                    continue
+                if exc is not OSError and issubclass(exc, OSError):
+                    self.assertEqual(reverse_mapping('builtins', name),
+                                     ('exceptions', 'OSError'))
+                else:
+                    self.assertEqual(reverse_mapping('builtins', name),
+                                     ('exceptions', name))
+                    self.assertEqual(mapping('exceptions', name),
+                                     ('builtins', name))
+
+        import multiprocessing.context
+        for name, exc in get_exceptions(multiprocessing.context):
+            with self.subTest(name):
+                self.assertEqual(reverse_mapping('multiprocessing.context', name),
+                                 ('multiprocessing', name))
+                self.assertEqual(mapping('multiprocessing', name),
+                                 ('multiprocessing.context', name))
+
+
 def test_main():
     tests = [PickleTests, PyPicklerTests, PyPersPicklerTests,
-             PyDispatchTableTests, PyChainDispatchTableTests]
+             PyDispatchTableTests, PyChainDispatchTableTests,
+             CompatPickleTests]
     if has_c_implementation:
         tests.extend([CPicklerTests, CPersPicklerTests,
                       CDumpPickle_LoadPickle, DumpPickle_CLoadPickle,