Follow-up to r91064 to also allow deep-copied blobs to be opened (also see...

Follow-up to r91064 to also allow deep-copied blobs to be opened (also see http://mail.zope.org/pipermail/zodb-dev/2008-August/012054.html).

NEWS.txt

@@ -4,6 +4,8 @@ Whats new in ZODB 3.8.1
 
 Bugs Fixed:
 
+- (beta 9) Fixed a bug to allow opening of deep-copied blobs.
+
 - (beta 9) Fixed bug #189542 by prepending the module to an undefined name.
 
 - (beta 8) If there is a failure while FileStorage is finalizing a transaction,

src/ZODB/blob.py

@@ -125,6 +125,9 @@ class Blob(persistent.Persistent):
         if self.writers:
             raise BlobError("Already opened for writing.")
 
+        if self.readers is None:
+            self.readers = []
+
         if mode == 'r':
             if self._current_filename() is None:
                 self._create_uncommitted_file()

src/ZODB/tests/testblob.py

@@ -140,6 +140,10 @@ class BlobCloneTests(BlobTests):
         clone = u.load()
         clone._p_invalidate()
 
+        # it should also be possible to open the cloned blob
+        # (even though it won't contain the original data)
+        clone.open()
+
 
 class BlobUndoTests(BlobTests):