From 404378f83432651429634d7e2a66d2b079397099 Mon Sep 17 00:00:00 2001
From: Skip Montanaro <skip@pobox.com>
Date: Fri, 2 Aug 2002 17:12:15 +0000
Subject: [PATCH] catch the situation where Berkeley DB is used to emulate
 dbm(3) library functions.  In this case, calling dbm.open("foo", "c")
 actually creates a file named "foo.db".

---
 Lib/whichdb.py | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/Lib/whichdb.py b/Lib/whichdb.py
index 8b31003d9b1..cc95ed512f5 100644
--- a/Lib/whichdb.py
+++ b/Lib/whichdb.py
@@ -1,6 +1,16 @@
 """Guess which db package to use to open a db file."""
 
 import os
+import struct
+
+try:
+    import dbm
+    _dbmerror = dbm.error
+except ImportError:
+    dbm = None
+    # just some sort of valid exception which might be raised in the
+    # dbm test
+    _dbmerror = IOError
 
 def whichdb(filename):
     """Guess which db package to use to open a db file.
@@ -15,8 +25,6 @@ def whichdb(filename):
     database using that module may still fail.
     """
 
-    import struct
-
     # Check for dbm first -- this has a .pag and a .dir file
     try:
         f = open(filename + os.extsep + "pag", "rb")
@@ -25,7 +33,20 @@ def whichdb(filename):
         f.close()
         return "dbm"
     except IOError:
-        pass
+        # some dbm emulations based on Berkeley DB generate a .db file
+        # some do not, but they should be caught by the dbhash checks
+        try:
+            f = open(filename + os.extsep + "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 dbm is not None:
+                d = dbm.open(filename)
+                d.close()
+                return "dbm"
+        except (IOError, _dbmerror):
+            pass
 
     # Check for dumbdbm next -- this has a .dir and and a .dat file
     try: