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- """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:
- return ""
-
- # Check for GNU dbm
- if magic == 0x13579ace:
- return "gdbm"
-
- # Check for BSD hash
- if magic in (0x00061561, 0x61150600):
- return "dbhash"
-
- # Unknown
- return ""
-