Add transact helper.

src/ZODB/transact.py

+##############################################################################
+#
+# Copyright (c) 2003 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE
+#
+##############################################################################
+"""Tools to simplify transactions within applications."""
+
+from ZODB.POSException import ReadConflictError, ConflictError
+
+def _commit(note):
+    t = get_transaction()
+    if note:
+        t.note(note)
+    t.commit()
+
+def transact(f, note=None, retries=5):
+    """Returns transactional version of function argument f.
+
+    Higher-order function that converts a regular function into
+    a transactional function.  The transactional function will
+    retry up to retries time before giving up.  If note, it will
+    be added to the transaction metadata when it commits.
+
+    The retries occur on ConflictErrors.  If some other
+    TransactionError occurs, the transaction will not be retried.
+    """
+
+    # XXX deal with ZEO disconnected errors?
+    
+    def g(*args, **kwargs):
+        while retries:
+            retries -= 1
+            try:
+                r = f(*args, **kwargs)
+            except ReadConflictError, msg:
+                get_transaction().abort()
+                if not retries:
+                    raise
+                continue
+            try:
+                _commit(note)
+            except ConflictError, msg:
+                get_transaction().abort()
+                if not retries:
+                    raise
+                continue
+            return r
+        raise RuntimeError, "couldn't commit transaction"
+    return g