gh-134004: Added the reorganize() methods to dbm.sqlite, dbm.dumb and shelve (GH-134028)

They are similar to the same named method in dbm.gnu.

Lib/dbm/dumb.py

@@ -9,7 +9,7 @@ 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)
+items is not reused exept if .reorganize() is called)
 
 - support concurrent access (currently, if two processes take turns making
 updates, they can mess up the index)
@@ -17,8 +17,6 @@ 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
@@ -289,6 +287,34 @@ class _Database(collections.abc.MutableMapping):
     def __exit__(self, *args):
         self.close()
 
+    def reorganize(self):
+        if self._readonly:
+            raise error('The database is opened for reading only')
+        self._verify_open()
+        # Ensure all changes are committed before reorganizing.
+        self._commit()
+        # Open file in r+ to allow changing in-place.
+        with _io.open(self._datfile, 'rb+') as f:
+            reorganize_pos = 0
+
+            # Iterate over existing keys, sorted by starting byte.
+            for key in sorted(self._index, key = lambda k: self._index[k][0]):
+                pos, siz = self._index[key]
+                f.seek(pos)
+                val = f.read(siz)
+
+                f.seek(reorganize_pos)
+                f.write(val)
+                self._index[key] = (reorganize_pos, siz)
+
+                blocks_occupied = (siz + _BLOCKSIZE - 1) // _BLOCKSIZE
+                reorganize_pos += blocks_occupied * _BLOCKSIZE
+
+            f.truncate(reorganize_pos)
+        # Commit changes to index, which were not in-place.
+        self._commit()
+
+
 
 def open(file, flag='c', mode=0o666):
     """Open the database file, filename, and return corresponding object.