Warn rather than fail if DB.open is called with an empty version string.

src/CHANGES.txt

@@ -30,6 +30,13 @@ Bugs Fixed
 - BlobStorage was not compatible with MVCC storages because the
   wrappers were being removed by each database connection.  Fixed.
 
+Features added back
+-------------------
+
+- Warn rather than fail if DB.open is called with an empty version
+  string.
+
+
 3.9.0b2 (2009-06-11)
 ====================
 

src/ZODB/DB.py

@@ -14,8 +14,6 @@
 """Database objects
 """
 
-import warnings
-
 import cPickle
 import cStringIO
 import sys
@@ -24,6 +22,7 @@ import logging
 import datetime
 import calendar
 import time
+import warnings
 
 from ZODB.broken import find_global
 from ZODB.utils import z64
@@ -728,6 +727,15 @@ class DB(object):
             raise ValueError(
                 'cannot open an historical connection in the future.')
 
+        if isinstance(transaction_manager, basestring):
+            if transaction_manager:
+                raise TypeError("Versions aren't supported.")
+            warnings.warn(
+                "A version string was passed to open.\n"
+                "The first argument is a transaction manager.",
+                DeprecationWarning, 2)
+            transaction_manager = None
+
         self._a()
         try:
             # result <- a connection

src/ZODB/tests/testDB.py

@@ -240,6 +240,23 @@ if sys.version_info >= (2, 6):
         >>> db.close()
         """
 
+def connection_allows_empty_version_for_idiots():
+    r"""
+    >>> import sys, StringIO
+    >>> stderr = sys.stderr
+    >>> sys.stderr = StringIO.StringIO()
+    >>> db = ZODB.DB('t.fs')
+    >>> c = db.open('')
+    >>> sys.stderr.getvalue() # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
+    '...: DeprecationWarning: A version string was passed to
+    open.\nThe first argument is a transaction manager...
+
+    >>> sys.stderr = stderr
+    >>> c.root()
+    {}
+    >>> db.close()
+    """
+
 def test_suite():
     s = unittest.makeSuite(DBTests)
     s.addTest(doctest.DocTestSuite(