Function to guess which db package created a database.
diff --git a/Lib/whichdb.py b/Lib/whichdb.py
new file mode 100644
index 0000000..3722e41
--- /dev/null
+++ b/Lib/whichdb.py
@@ -0,0 +1,60 @@
+"""Guess which db package to use to open a db file."""
+
+import struct
+
+def whichdb(filename):
+ """Guess which db package to use to open a db file.
+
+ Return values:
+
+ - None if the database file can't be read;
+ - empty string if the file can be read but can't be recognized
+ - the module name (e.g. "dbm" or "gdbm") if recognized.
+
+ Importing the given module may still fail, and opening the
+ database using that module may still fail.
+ """
+
+ # Check for dbm first -- this has a .pag and a .dir file
+ try:
+ f = open(filename + ".pag", "rb")
+ f.close()
+ f = open(filename + ".dir", "rb")
+ f.close()
+ return "dbm"
+ except IOError:
+ pass
+
+ # See if the file exists, return None if not
+ try:
+ f = open(filename, "rb")
+ except IOError:
+ return None
+
+ # Read the first 4 bytes of the file -- the magic number
+ s = f.read(4)
+ f.close()
+
+ # Return "" if not at least 4 bytes
+ if len(s) != 4:
+ return ""
+
+ # Convert to 4-byte int in native byte order -- return "" if impossible
+ try:
+ (magic,) = struct.unpack("l", s)
+ except struct.error:
+ try:
+ (magic,) = struct.unpack("i", s)
+ except struct.error:
+ return ""
+
+ # Check for GNU dbm
+ if magic == 0x13579ace:
+ return "gdbm"
+
+ # Check for BSD hash
+ if magic == 0x061561:
+ return "dbhash"
+
+ # Unknown
+ return ""