diff --git a/Lib/dbm/__init__.py b/Lib/dbm/__init__.py
new file mode 100644
index 000000000..f65da521a
--- /dev/null
+++ b/Lib/dbm/__init__.py
@@ -0,0 +1,189 @@
+"""Generic interface to all dbm clones.
+
+Use
+
+        import dbm
+        d = dbm.open(file, 'w', 0o666)
+
+The returned object is a dbm.gnu, dbm.ndbm or dbm.dumb object, dependent on the
+type of database being opened (determined by the whichdb function) in the case
+of an existing dbm. If the dbm does not exist and the create or new flag ('c'
+or 'n') was specified, the dbm type will be determined by the availability of
+the modules (tested in the above order).
+
+It has the following interface (key and data are strings):
+
+        d[key] = data   # store data at key (may override data at
+                        # existing key)
+        data = d[key]   # retrieve data at key (raise KeyError if no
+                        # such key)
+        del d[key]      # delete data stored at key (raises KeyError
+                        # if no such key)
+        flag = key in d # true if the key exists
+        list = d.keys() # return a list of all existing keys (slow!)
+
+Future versions may change the order in which implementations are
+tested for existence, and add interfaces to other dbm-like
+implementations.
+"""
+
+__all__ = ['open', 'whichdb', 'error']
+
+import io
+import os
+import struct
+import sys
+
+
+class error(Exception):
+    pass
+
+_names = ['dbm.gnu', 'dbm.ndbm', 'dbm.dumb']
+_defaultmod = None
+_modules = {}
+
+error = (error, OSError)
+
+try:
+    from dbm import ndbm
+except ImportError:
+    ndbm = None
+
+
+def open(file, flag='r', mode=0o666):
+    """Open or create database at path given by *file*.
+
+    Optional argument *flag* can be 'r' (default) for read-only access, 'w'
+    for read-write access of an existing database, 'c' for read-write access
+    to a new or existing database, and 'n' for read-write access to a new
+    database.
+
+    Note: 'r' and 'w' fail if the database doesn't exist; 'c' creates it
+    only if it doesn't exist; and 'n' always creates a new database.
+    """
+    global _defaultmod
+    if _defaultmod is None:
+        for name in _names:
+            try:
+                mod = __import__(name, fromlist=['open'])
+            except ImportError:
+                continue
+            if not _defaultmod:
+                _defaultmod = mod
+            _modules[name] = mod
+        if not _defaultmod:
+            raise ImportError("no dbm clone found; tried %s" % _names)
+
+    # guess the type of an existing database, if not creating a new one
+    result = whichdb(file) if 'n' not in flag else None
+    if result is None:
+        # db doesn't exist or 'n' flag was specified to create a new db
+        if 'c' in flag or 'n' in flag:
+            # file doesn't exist and the new flag was used so use default type
+            mod = _defaultmod
+        else:
+            raise error[0]("db file doesn't exist; "
+                           "use 'c' or 'n' flag to create a new db")
+    elif result == "":
+        # db type cannot be determined
+        raise error[0]("db type could not be determined")
+    elif result not in _modules:
+        raise error[0]("db type is {0}, but the module is not "
+                       "available".format(result))
+    else:
+        mod = _modules[result]
+    return mod.open(file, flag, mode)
+
+
+def whichdb(filename):
+    """Guess which db package to use to open a db file.
+
+    Return values:
+
+    - None if the database file can't be read;
+    - empty string if the file can be read but can't be recognized
+    - the name of the dbm submodule (e.g. "ndbm" or "gnu") if recognized.
+
+    Importing the given module may still fail, and opening the
+    database using that module may still fail.
+    """
+
+    # Check for ndbm first -- this has a .pag and a .dir file
+    try:
+        f = io.open(filename + ".pag", "rb")
+        f.close()
+        f = io.open(filename + ".dir", "rb")
+        f.close()
+        return "dbm.ndbm"
+    except OSError:
+        # some dbm emulations based on Berkeley DB generate a .db file
+        # some do not, but they should be caught by the bsd checks
+        try:
+            f = io.open(filename + ".db", "rb")
+            f.close()
+            # guarantee we can actually open the file using dbm
+            # kind of overkill, but since we are dealing with emulations
+            # it seems like a prudent step
+            if ndbm is not None:
+                d = ndbm.open(filename)
+                d.close()
+                return "dbm.ndbm"
+        except OSError:
+            pass
+
+    # Check for dumbdbm next -- this has a .dir and a .dat file
+    try:
+        # First check for presence of files
+        os.stat(filename + ".dat")
+        size = os.stat(filename + ".dir").st_size
+        # dumbdbm files with no keys are empty
+        if size == 0:
+            return "dbm.dumb"
+        f = io.open(filename + ".dir", "rb")
+        try:
+            if f.read(1) in (b"'", b'"'):
+                return "dbm.dumb"
+        finally:
+            f.close()
+    except OSError:
+        pass
+
+    # See if the file exists, return None if not
+    try:
+        f = io.open(filename, "rb")
+    except OSError:
+        return None
+
+    with f:
+        # Read the start of the file -- the magic number
+        s16 = f.read(16)
+    s = s16[0:4]
+
+    # Return "" if not at least 4 bytes
+    if len(s) != 4:
+        return ""
+
+    # Convert to 4-byte int in native byte order -- return "" if impossible
+    try:
+        (magic,) = struct.unpack("=l", s)
+    except struct.error:
+        return ""
+
+    # Check for GNU dbm
+    if magic in (0x13579ace, 0x13579acd, 0x13579acf):
+        return "dbm.gnu"
+
+    # Later versions of Berkeley db hash file have a 12-byte pad in
+    # front of the file type
+    try:
+        (magic,) = struct.unpack("=l", s16[-4:])
+    except struct.error:
+        return ""
+
+    # Unknown
+    return ""
+
+
+if __name__ == "__main__":
+    for filename in sys.argv[1:]:
+        print(whichdb(filename) or "UNKNOWN", filename)
diff --git a/Lib/dbm/dumb.py b/Lib/dbm/dumb.py
new file mode 100644
index 000000000..864ad371e
--- /dev/null
+++ b/Lib/dbm/dumb.py
@@ -0,0 +1,316 @@
+"""A dumb and slow but simple dbm clone.
+
+For database spam, spam.dir contains the index (a text file),
+spam.bak *may* contain a backup of the index (also a text file),
+while spam.dat contains the data (a binary file).
+
+XXX TO DO:
+
+- seems to contain a bug when updating...
+
+- reclaim free space (currently, space once occupied by deleted or expanded
+items is never reused)
+
+- support concurrent access (currently, if two processes take turns making
+updates, they can mess up the index)
+
+- support efficient access to large databases (currently, the whole index
+is read when the database is opened, and some updates rewrite the whole index)
+
+- support opening for read-only (flag = 'm')
+
+"""
+
+import ast as _ast
+import io as _io
+import os as _os
+import collections.abc
+
+__all__ = ["error", "open"]
+
+_BLOCKSIZE = 512
+
+error = OSError
+
+class _Database(collections.abc.MutableMapping):
+
+    # The on-disk directory and data files can remain in mutually
+    # inconsistent states for an arbitrarily long time (see comments
+    # at the end of __setitem__).  This is only repaired when _commit()
+    # gets called.  One place _commit() gets called is from __del__(),
+    # and if that occurs at program shutdown time, module globals may
+    # already have gotten rebound to None.  Since it's crucial that
+    # _commit() finish successfully, we can't ignore shutdown races
+    # here, and _commit() must not reference any globals.
+    _os = _os       # for _commit()
+    _io = _io       # for _commit()
+
+    def __init__(self, filebasename, mode, flag='c'):
+        self._mode = mode
+        self._readonly = (flag == 'r')
+
+        # The directory file is a text file.  Each line looks like
+        #    "%r, (%d, %d)\n" % (key, pos, siz)
+        # where key is the string key, pos is the offset into the dat
+        # file of the associated value's first byte, and siz is the number
+        # of bytes in the associated value.
+        self._dirfile = filebasename + '.dir'
+
+        # The data file is a binary file pointed into by the directory
+        # file, and holds the values associated with keys.  Each value
+        # begins at a _BLOCKSIZE-aligned byte offset, and is a raw
+        # binary 8-bit string value.
+        self._datfile = filebasename + '.dat'
+        self._bakfile = filebasename + '.bak'
+
+        # The index is an in-memory dict, mirroring the directory file.
+        self._index = None  # maps keys to (pos, siz) pairs
+
+        # Handle the creation
+        self._create(flag)
+        self._update(flag)
+
+    def _create(self, flag):
+        if flag == 'n':
+            for filename in (self._datfile, self._bakfile, self._dirfile):
+                try:
+                    _os.remove(filename)
+                except OSError:
+                    pass
+        # Mod by Jack: create data file if needed
+        try:
+            f = _io.open(self._datfile, 'r', encoding="Latin-1")
+        except OSError:
+            if flag not in ('c', 'n'):
+                raise
+            with _io.open(self._datfile, 'w', encoding="Latin-1") as f:
+                self._chmod(self._datfile)
+        else:
+            f.close()
+
+    # Read directory file into the in-memory index dict.
+    def _update(self, flag):
+        self._modified = False
+        self._index = {}
+        try:
+            f = _io.open(self._dirfile, 'r', encoding="Latin-1")
+        except OSError:
+            if flag not in ('c', 'n'):
+                raise
+            self._modified = True
+        else:
+            with f:
+                for line in f:
+                    line = line.rstrip()
+                    key, pos_and_siz_pair = _ast.literal_eval(line)
+                    key = key.encode('Latin-1')
+                    self._index[key] = pos_and_siz_pair
+
+    # Write the index dict to the directory file.  The original directory
+    # file (if any) is renamed with a .bak extension first.  If a .bak
+    # file currently exists, it's deleted.
+    def _commit(self):
+        # CAUTION:  It's vital that _commit() succeed, and _commit() can
+        # be called from __del__().  Therefore we must never reference a
+        # global in this routine.
+        if self._index is None or not self._modified:
+            return  # nothing to do
+
+        try:
+            self._os.unlink(self._bakfile)
+        except OSError:
+            pass
+
+        try:
+            self._os.rename(self._dirfile, self._bakfile)
+        except OSError:
+            pass
+
+        with self._io.open(self._dirfile, 'w', encoding="Latin-1") as f:
+            self._chmod(self._dirfile)
+            for key, pos_and_siz_pair in self._index.items():
+                # Use Latin-1 since it has no qualms with any value in any
+                # position; UTF-8, though, does care sometimes.
+                entry = "%r, %r\n" % (key.decode('Latin-1'), pos_and_siz_pair)
+                f.write(entry)
+
+    sync = _commit
+
+    def _verify_open(self):
+        if self._index is None:
+            raise error('DBM object has already been closed')
+
+    def __getitem__(self, key):
+        if isinstance(key, str):
+            key = key.encode('utf-8')
+        self._verify_open()
+        pos, siz = self._index[key]     # may raise KeyError
+        with _io.open(self._datfile, 'rb') as f:
+            f.seek(pos)
+            dat = f.read(siz)
+        return dat
+
+    # Append val to the data file, starting at a _BLOCKSIZE-aligned
+    # offset.  The data file is first padded with NUL bytes (if needed)
+    # to get to an aligned offset.  Return pair
+    #     (starting offset of val, len(val))
+    def _addval(self, val):
+        with _io.open(self._datfile, 'rb+') as f:
+            f.seek(0, 2)
+            pos = int(f.tell())
+            npos = ((pos + _BLOCKSIZE - 1) // _BLOCKSIZE) * _BLOCKSIZE
+            f.write(b'\0'*(npos-pos))
+            pos = npos
+            f.write(val)
+        return (pos, len(val))
+
+    # Write val to the data file, starting at offset pos.  The caller
+    # is responsible for ensuring that there's enough room starting at
+    # pos to hold val, without overwriting some other value.  Return
+    # pair (pos, len(val)).
+    def _setval(self, pos, val):
+        with _io.open(self._datfile, 'rb+') as f:
+            f.seek(pos)
+            f.write(val)
+        return (pos, len(val))
+
+    # key is a new key whose associated value starts in the data file
+    # at offset pos and with length siz.  Add an index record to
+    # the in-memory index dict, and append one to the directory file.
+    def _addkey(self, key, pos_and_siz_pair):
+        self._index[key] = pos_and_siz_pair
+        with _io.open(self._dirfile, 'a', encoding="Latin-1") as f:
+            self._chmod(self._dirfile)
+            f.write("%r, %r\n" % (key.decode("Latin-1"), pos_and_siz_pair))
+
+    def __setitem__(self, key, val):
+        if self._readonly:
+            raise error('The database is opened for reading only')
+        if isinstance(key, str):
+            key = key.encode('utf-8')
+        elif not isinstance(key, (bytes, bytearray)):
+            raise TypeError("keys must be bytes or strings")
+        if isinstance(val, str):
+            val = val.encode('utf-8')
+        elif not isinstance(val, (bytes, bytearray)):
+            raise TypeError("values must be bytes or strings")
+        self._verify_open()
+        self._modified = True
+        if key not in self._index:
+            self._addkey(key, self._addval(val))
+        else:
+            # See whether the new value is small enough to fit in the
+            # (padded) space currently occupied by the old value.
+            pos, siz = self._index[key]
+            oldblocks = (siz + _BLOCKSIZE - 1) // _BLOCKSIZE
+            newblocks = (len(val) + _BLOCKSIZE - 1) // _BLOCKSIZE
+            if newblocks <= oldblocks:
+                self._index[key] = self._setval(pos, val)
+            else:
+                # The new value doesn't fit in the (padded) space used
+                # by the old value.  The blocks used by the old value are
+                # forever lost.
+                self._index[key] = self._addval(val)
+
+            # Note that _index may be out of synch with the directory
+            # file now:  _setval() and _addval() don't update the directory
+            # file.  This also means that the on-disk directory and data
+            # files are in a mutually inconsistent state, and they'll
+            # remain that way until _commit() is called.  Note that this
+            # is a disaster (for the database) if the program crashes
+            # (so that _commit() never gets called).
+
+    def __delitem__(self, key):
+        if self._readonly:
+            raise error('The database is opened for reading only')
+        if isinstance(key, str):
+            key = key.encode('utf-8')
+        self._verify_open()
+        self._modified = True
+        # The blocks used by the associated value are lost.
+        del self._index[key]
+        # XXX It's unclear why we do a _commit() here (the code always
+        # XXX has, so I'm not changing it).  __setitem__ doesn't try to
+        # XXX keep the directory file in synch.  Why should we?  Or
+        # XXX why shouldn't __setitem__?
+        self._commit()
+
+    def keys(self):
+        try:
+            return list(self._index)
+        except TypeError:
+            raise error('DBM object has already been closed') from None
+
+    def items(self):
+        self._verify_open()
+        return [(key, self[key]) for key in self._index.keys()]
+
+    def __contains__(self, key):
+        if isinstance(key, str):
+            key = key.encode('utf-8')
+        try:
+            return key in self._index
+        except TypeError:
+            if self._index is None:
+                raise error('DBM object has already been closed') from None
+            else:
+                raise
+
+    def iterkeys(self):
+        try:
+            return iter(self._index)
+        except TypeError:
+            raise error('DBM object has already been closed') from None
+    __iter__ = iterkeys
+
+    def __len__(self):
+        try:
+            return len(self._index)
+        except TypeError:
+            raise error('DBM object has already been closed') from None
+
+    def close(self):
+        try:
+            self._commit()
+        finally:
+            self._index = self._datfile = self._dirfile = self._bakfile = None
+
+    __del__ = close
+
+    def _chmod(self, file):
+        self._os.chmod(file, self._mode)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+def open(file, flag='c', mode=0o666):
+    """Open the database file, filename, and return corresponding object.
+
+    The flag argument, used to control how the database is opened in the
+    other DBM implementations, supports only the semantics of 'c' and 'n'
+    values.  Other values will default to the semantics of 'c' value:
+    the database will always opened for update and will be created if it
+    does not exist.
+
+    The optional mode argument is the UNIX mode of the file, used only when
+    the database has to be created.  It defaults to octal code 0o666 (and
+    will be modified by the prevailing umask).
+
+    """
+
+    # Modify mode depending on the umask
+    try:
+        um = _os.umask(0)
+        _os.umask(um)
+    except AttributeError:
+        pass
+    else:
+        # Turn off any bits that are set in the umask
+        mode = mode & (~um)
+    if flag not in ('r', 'w', 'c', 'n'):
+        raise ValueError("Flag must be one of 'r', 'w', 'c', or 'n'")
+    return _Database(file, mode, flag=flag)
diff --git a/Lib/test/test_dbm.py b/Lib/test/test_dbm.py
new file mode 100644
index 000000000..571da973a
--- /dev/null
+++ b/Lib/test/test_dbm.py
@@ -0,0 +1,212 @@
+"""Test script for the dbm.open function based on testdumbdbm.py"""
+
+import unittest
+import glob
+import test.support
+
+# Skip tests if dbm module doesn't exist.
+dbm = test.support.import_module('dbm')
+
+try:
+    from dbm import ndbm
+except ImportError:
+    ndbm = None
+
+_fname = test.support.TESTFN
+
+#
+# Iterates over every database module supported by dbm currently available,
+# setting dbm to use each in turn, and yielding that module
+#
+def dbm_iterator():
+    for name in dbm._names:
+        try:
+            mod = __import__(name, fromlist=['open'])
+        except ImportError:
+            continue
+        dbm._modules[name] = mod
+        yield mod
+
+#
+# Clean up all scratch databases we might have created during testing
+#
+def delete_files():
+    # we don't know the precise name the underlying database uses
+    # so we use glob to locate all names
+    for f in glob.glob(glob.escape(_fname) + "*"):
+        test.support.unlink(f)
+
+
+class AnyDBMTestCase:
+    _dict = {'a': b'Python:',
+             'b': b'Programming',
+             'c': b'the',
+             'd': b'way',
+             'f': b'Guido',
+             'g': b'intended',
+             }
+
+    def init_db(self):
+        f = dbm.open(_fname, 'n')
+        for k in self._dict:
+            f[k.encode("ascii")] = self._dict[k]
+        f.close()
+
+    def keys_helper(self, f):
+        keys = sorted(k.decode("ascii") for k in f.keys())
+        dkeys = sorted(self._dict.keys())
+        self.assertEqual(keys, dkeys)
+        return keys
+
+    def test_error(self):
+        self.assertTrue(issubclass(self.module.error, OSError))
+
+    def test_anydbm_not_existing(self):
+        self.assertRaises(dbm.error, dbm.open, _fname)
+
+    def test_anydbm_creation(self):
+        f = dbm.open(_fname, 'c')
+        self.assertEqual(list(f.keys()), [])
+        for key in self._dict:
+            f[key.encode("ascii")] = self._dict[key]
+        self.read_helper(f)
+        f.close()
+
+    def test_anydbm_creation_n_file_exists_with_invalid_contents(self):
+        # create an empty file
+        test.support.create_empty_file(_fname)
+        with dbm.open(_fname, 'n') as f:
+            self.assertEqual(len(f), 0)
+
+    def test_anydbm_modification(self):
+        self.init_db()
+        f = dbm.open(_fname, 'c')
+        self._dict['g'] = f[b'g'] = b"indented"
+        self.read_helper(f)
+        # setdefault() works as in the dict interface
+        self.assertEqual(f.setdefault(b'xxx', b'foo'), b'foo')
+        self.assertEqual(f[b'xxx'], b'foo')
+        f.close()
+
+    def test_anydbm_read(self):
+        self.init_db()
+        f = dbm.open(_fname, 'r')
+        self.read_helper(f)
+        # get() works as in the dict interface
+        self.assertEqual(f.get(b'a'), self._dict['a'])
+        self.assertEqual(f.get(b'xxx', b'foo'), b'foo')
+        self.assertIsNone(f.get(b'xxx'))
+        with self.assertRaises(KeyError):
+            f[b'xxx']
+        f.close()
+
+    def test_anydbm_keys(self):
+        self.init_db()
+        f = dbm.open(_fname, 'r')
+        keys = self.keys_helper(f)
+        f.close()
+
+    def test_empty_value(self):
+        if getattr(dbm._defaultmod, 'library', None) == 'Berkeley DB':
+            self.skipTest("Berkeley DB doesn't distinguish the empty value "
+                          "from the absent one")
+        f = dbm.open(_fname, 'c')
+        self.assertEqual(f.keys(), [])
+        f[b'empty'] = b''
+        self.assertEqual(f.keys(), [b'empty'])
+        self.assertIn(b'empty', f)
+        self.assertEqual(f[b'empty'], b'')
+        self.assertEqual(f.get(b'empty'), b'')
+        self.assertEqual(f.setdefault(b'empty'), b'')
+        f.close()
+
+    def test_anydbm_access(self):
+        self.init_db()
+        f = dbm.open(_fname, 'r')
+        key = "a".encode("ascii")
+        self.assertIn(key, f)
+        assert(f[key] == b"Python:")
+        f.close()
+
+    def read_helper(self, f):
+        keys = self.keys_helper(f)
+        for key in self._dict:
+            self.assertEqual(self._dict[key], f[key.encode("ascii")])
+
+    def tearDown(self):
+        delete_files()
+
+    def setUp(self):
+        dbm._defaultmod = self.module
+        delete_files()
+
+
+class WhichDBTestCase(unittest.TestCase):
+    def test_whichdb(self):
+        for module in dbm_iterator():
+            # Check whether whichdb correctly guesses module name
+            # for databases opened with "module" module.
+            # Try with empty files first
+            name = module.__name__
+            if name == 'dbm.dumb':
+                continue   # whichdb can't support dbm.dumb
+            delete_files()
+            f = module.open(_fname, 'c')
+            f.close()
+            self.assertEqual(name, self.dbm.whichdb(_fname))
+            # Now add a key
+            f = module.open(_fname, 'w')
+            f[b"1"] = b"1"
+            # and test that we can find it
+            self.assertIn(b"1", f)
+            # and read it
+            self.assertEqual(f[b"1"], b"1")
+            f.close()
+            self.assertEqual(name, self.dbm.whichdb(_fname))
+
+    @unittest.skipUnless(ndbm, reason='Test requires ndbm')
+    def test_whichdb_ndbm(self):
+        # Issue 17198: check that ndbm which is referenced in whichdb is defined
+        db_file = '{}_ndbm.db'.format(_fname)
+        with open(db_file, 'w'):
+            self.addCleanup(test.support.unlink, db_file)
+        self.assertIsNone(self.dbm.whichdb(db_file[:-3]))
+
+    def tearDown(self):
+        delete_files()
+
+    def setUp(self):
+        delete_files()
+        self.filename = test.support.TESTFN
+        self.d = dbm.open(self.filename, 'c')
+        self.d.close()
+        self.dbm = test.support.import_fresh_module('dbm')
+
+    def test_keys(self):
+        self.d = dbm.open(self.filename, 'c')
+        self.assertEqual(self.d.keys(), [])
+        a = [(b'a', b'b'), (b'12345678910', b'019237410982340912840198242')]
+        for k, v in a:
+            self.d[k] = v
+        self.assertEqual(sorted(self.d.keys()), sorted(k for (k, v) in a))
+        for k, v in a:
+            self.assertIn(k, self.d)
+            self.assertEqual(self.d[k], v)
+        self.assertNotIn(b'xxx', self.d)
+        self.assertRaises(KeyError, lambda: self.d[b'xxx'])
+        self.d.close()
+
+
+def load_tests(loader, tests, pattern):
+    classes = []
+    for mod in dbm_iterator():
+        classes.append(type("TestCase-" + mod.__name__,
+                            (AnyDBMTestCase, unittest.TestCase),
+                            {'module': mod}))
+    suites = [unittest.makeSuite(c) for c in classes]
+
+    tests.addTests(suites)
+    return tests
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/Lib/test/test_dbm_dumb.py b/Lib/test/test_dbm_dumb.py
new file mode 100644
index 000000000..0a6077820
--- /dev/null
+++ b/Lib/test/test_dbm_dumb.py
@@ -0,0 +1,303 @@
+"""Test script for the dumbdbm module
+   Original by Roger E. Masse
+"""
+
+import contextlib
+import io
+import operator
+import os
+import stat
+import unittest
+import dbm.dumb as dumbdbm
+from test import support
+from functools import partial
+
+_fname = support.TESTFN
+
+def _delete_files():
+    for ext in [".dir", ".dat", ".bak"]:
+        try:
+            os.unlink(_fname + ext)
+        except OSError:
+            pass
+
+class DumbDBMTestCase(unittest.TestCase):
+    _dict = {b'0': b'',
+             b'a': b'Python:',
+             b'b': b'Programming',
+             b'c': b'the',
+             b'd': b'way',
+             b'f': b'Guido',
+             b'g': b'intended',
+             '\u00fc'.encode('utf-8') : b'!',
+             }
+
+    def test_dumbdbm_creation(self):
+        with contextlib.closing(dumbdbm.open(_fname, 'c')) as f:
+            self.assertEqual(list(f.keys()), [])
+            for key in self._dict:
+                f[key] = self._dict[key]
+            self.read_helper(f)
+
+    @unittest.skipUnless(hasattr(os, 'umask'), 'test needs os.umask()')
+    def test_dumbdbm_creation_mode(self):
+        try:
+            old_umask = os.umask(0o002)
+            f = dumbdbm.open(_fname, 'c', 0o637)
+            f.close()
+        finally:
+            os.umask(old_umask)
+
+        expected_mode = 0o635
+        if os.name != 'posix':
+            # Windows only supports setting the read-only attribute.
+            # This shouldn't fail, but doesn't work like Unix either.
+            expected_mode = 0o666
+
+        import stat
+        st = os.stat(_fname + '.dat')
+        self.assertEqual(stat.S_IMODE(st.st_mode), expected_mode)
+        st = os.stat(_fname + '.dir')
+        self.assertEqual(stat.S_IMODE(st.st_mode), expected_mode)
+
+    def test_close_twice(self):
+        f = dumbdbm.open(_fname)
+        f[b'a'] = b'b'
+        self.assertEqual(f[b'a'], b'b')
+        f.close()
+        f.close()
+
+    def test_dumbdbm_modification(self):
+        self.init_db()
+        with contextlib.closing(dumbdbm.open(_fname, 'w')) as f:
+            self._dict[b'g'] = f[b'g'] = b"indented"
+            self.read_helper(f)
+            # setdefault() works as in the dict interface
+            self.assertEqual(f.setdefault(b'xxx', b'foo'), b'foo')
+            self.assertEqual(f[b'xxx'], b'foo')
+
+    def test_dumbdbm_read(self):
+        self.init_db()
+        with contextlib.closing(dumbdbm.open(_fname, 'r')) as f:
+            self.read_helper(f)
+            with self.assertRaisesRegex(dumbdbm.error,
+                                    'The database is opened for reading only'):
+                f[b'g'] = b'x'
+            with self.assertRaisesRegex(dumbdbm.error,
+                                    'The database is opened for reading only'):
+                del f[b'a']
+            # get() works as in the dict interface
+            self.assertEqual(f.get(b'a'), self._dict[b'a'])
+            self.assertEqual(f.get(b'xxx', b'foo'), b'foo')
+            self.assertIsNone(f.get(b'xxx'))
+            with self.assertRaises(KeyError):
+                f[b'xxx']
+
+    def test_dumbdbm_keys(self):
+        self.init_db()
+        with contextlib.closing(dumbdbm.open(_fname)) as f:
+            keys = self.keys_helper(f)
+
+    def test_write_contains(self):
+        with contextlib.closing(dumbdbm.open(_fname)) as f:
+            f[b'1'] = b'hello'
+            self.assertIn(b'1', f)
+
+    def test_write_write_read(self):
+        # test for bug #482460
+        with contextlib.closing(dumbdbm.open(_fname)) as f:
+            f[b'1'] = b'hello'
+            f[b'1'] = b'hello2'
+        with contextlib.closing(dumbdbm.open(_fname)) as f:
+            self.assertEqual(f[b'1'], b'hello2')
+
+    def test_str_read(self):
+        self.init_db()
+        with contextlib.closing(dumbdbm.open(_fname, 'r')) as f:
+            self.assertEqual(f['\u00fc'], self._dict['\u00fc'.encode('utf-8')])
+
+    def test_str_write_contains(self):
+        self.init_db()
+        with contextlib.closing(dumbdbm.open(_fname)) as f:
+            f['\u00fc'] = b'!'
+            f['1'] = 'a'
+        with contextlib.closing(dumbdbm.open(_fname, 'r')) as f:
+            self.assertIn('\u00fc', f)
+            self.assertEqual(f['\u00fc'.encode('utf-8')],
+                             self._dict['\u00fc'.encode('utf-8')])
+            self.assertEqual(f[b'1'], b'a')
+
+    def test_line_endings(self):
+        # test for bug #1172763: dumbdbm would die if the line endings
+        # weren't what was expected.
+        with contextlib.closing(dumbdbm.open(_fname)) as f:
+            f[b'1'] = b'hello'
+            f[b'2'] = b'hello2'
+
+        # Mangle the file by changing the line separator to Windows or Unix
+        with io.open(_fname + '.dir', 'rb') as file:
+            data = file.read()
+        if os.linesep == '\n':
+            data = data.replace(b'\n', b'\r\n')
+        else:
+            data = data.replace(b'\r\n', b'\n')
+        with io.open(_fname + '.dir', 'wb') as file:
+            file.write(data)
+
+        f = dumbdbm.open(_fname)
+        self.assertEqual(f[b'1'], b'hello')
+        self.assertEqual(f[b'2'], b'hello2')
+
+
+    def read_helper(self, f):
+        keys = self.keys_helper(f)
+        for key in self._dict:
+            self.assertEqual(self._dict[key], f[key])
+
+    def init_db(self):
+        with contextlib.closing(dumbdbm.open(_fname, 'n')) as f:
+            for k in self._dict:
+                f[k] = self._dict[k]
+
+    def keys_helper(self, f):
+        keys = sorted(f.keys())
+        dkeys = sorted(self._dict.keys())
+        self.assertEqual(keys, dkeys)
+        return keys
+
+    # Perform randomized operations.  This doesn't make assumptions about
+    # what *might* fail.
+    def test_random(self):
+        import random
+        d = {}  # mirror the database
+        for dummy in range(5):
+            with contextlib.closing(dumbdbm.open(_fname)) as f:
+                for dummy in range(100):
+                    k = random.choice('abcdefghijklm')
+                    if random.random() < 0.2:
+                        if k in d:
+                            del d[k]
+                            del f[k]
+                    else:
+                        v = random.choice((b'a', b'b', b'c')) * random.randrange(10000)
+                        d[k] = v
+                        f[k] = v
+                        self.assertEqual(f[k], v)
+
+            with contextlib.closing(dumbdbm.open(_fname)) as f:
+                expected = sorted((k.encode("latin-1"), v) for k, v in d.items())
+                got = sorted(f.items())
+                self.assertEqual(expected, got)
+
+    def test_context_manager(self):
+        with dumbdbm.open(_fname, 'c') as db:
+            db["dumbdbm context manager"] = "context manager"
+
+        with dumbdbm.open(_fname, 'r') as db:
+            self.assertEqual(list(db.keys()), [b"dumbdbm context manager"])
+
+        with self.assertRaises(dumbdbm.error):
+            db.keys()
+
+    def test_check_closed(self):
+        f = dumbdbm.open(_fname, 'c')
+        f.close()
+
+        for meth in (partial(operator.delitem, f),
+                     partial(operator.setitem, f, 'b'),
+                     partial(operator.getitem, f),
+                     partial(operator.contains, f)):
+            with self.assertRaises(dumbdbm.error) as cm:
+                meth('test')
+            self.assertEqual(str(cm.exception),
+                             "DBM object has already been closed")
+
+        for meth in (operator.methodcaller('keys'),
+                     operator.methodcaller('iterkeys'),
+                     operator.methodcaller('items'),
+                     len):
+            with self.assertRaises(dumbdbm.error) as cm:
+                meth(f)
+            self.assertEqual(str(cm.exception),
+                             "DBM object has already been closed")
+
+    def test_create_new(self):
+        with dumbdbm.open(_fname, 'n') as f:
+            for k in self._dict:
+                f[k] = self._dict[k]
+
+        with dumbdbm.open(_fname, 'n') as f:
+            self.assertEqual(f.keys(), [])
+
+    def test_eval(self):
+        with open(_fname + '.dir', 'w') as stream:
+            stream.write("str(print('Hacked!')), 0\n")
+        with support.captured_stdout() as stdout:
+            with self.assertRaises(ValueError):
+                with dumbdbm.open(_fname) as f:
+                    pass
+            self.assertEqual(stdout.getvalue(), '')
+
+    def test_missing_data(self):
+        for value in ('r', 'w'):
+            _delete_files()
+            with self.assertRaises(FileNotFoundError):
+                dumbdbm.open(_fname, value)
+            self.assertFalse(os.path.exists(_fname + '.dir'))
+            self.assertFalse(os.path.exists(_fname + '.bak'))
+
+    def test_missing_index(self):
+        with dumbdbm.open(_fname, 'n') as f:
+            pass
+        os.unlink(_fname + '.dir')
+        for value in ('r', 'w'):
+            with self.assertRaises(FileNotFoundError):
+                dumbdbm.open(_fname, value)
+            self.assertFalse(os.path.exists(_fname + '.dir'))
+            self.assertFalse(os.path.exists(_fname + '.bak'))
+
+    def test_invalid_flag(self):
+        for flag in ('x', 'rf', None):
+            with self.assertRaisesRegex(ValueError,
+                                        "Flag must be one of "
+                                        "'r', 'w', 'c', or 'n'"):
+                dumbdbm.open(_fname, flag)
+
+    def test_readonly_files(self):
+        with support.temp_dir() as dir:
+            fname = os.path.join(dir, 'db')
+            with dumbdbm.open(fname, 'n') as f:
+                self.assertEqual(list(f.keys()), [])
+                for key in self._dict:
+                    f[key] = self._dict[key]
+            os.chmod(fname + ".dir", stat.S_IRUSR)
+            os.chmod(fname + ".dat", stat.S_IRUSR)
+            os.chmod(dir, stat.S_IRUSR|stat.S_IXUSR)
+            with dumbdbm.open(fname, 'r') as f:
+                self.assertEqual(sorted(f.keys()), sorted(self._dict))
+                f.close()  # don't write
+
+    @unittest.skipUnless(support.TESTFN_NONASCII,
+                         'requires OS support of non-ASCII encodings')
+    def test_nonascii_filename(self):
+        filename = support.TESTFN_NONASCII
+        for suffix in ['.dir', '.dat', '.bak']:
+            self.addCleanup(support.unlink, filename + suffix)
+        with dumbdbm.open(filename, 'c') as db:
+            db[b'key'] = b'value'
+        self.assertTrue(os.path.exists(filename + '.dat'))
+        self.assertTrue(os.path.exists(filename + '.dir'))
+        with dumbdbm.open(filename, 'r') as db:
+            self.assertEqual(list(db.keys()), [b'key'])
+            self.assertTrue(b'key' in db)
+            self.assertEqual(db[b'key'], b'value')
+
+    def tearDown(self):
+        _delete_files()
+
+    def setUp(self):
+        _delete_files()
+
+
+if __name__ == "__main__":
+    unittest.main()