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v0.8.1
Revision d499004860fc74cd95f40b786133229f1d0550bf authored by Guido van Rossum on 28 December 1997, 04:21:20 UTC, committed by Guido van Rossum on 28 December 1997, 04:21:20 UTC 
Solve two annoying problems with ftp URLs for Jack: when repeated
 
retrieving files from the same host and directory, you had to close
the previous instance before opening a new one; and retrieving a
non-existent file would return an empty file.  (The latter fix relies
on maybe an undocumented property of NLST -- NLST of a file returns
just that file, while NLST of a non-existent file returns nothing.  A
side effect, unfortunately, seems to be that now ftp-retrieving an
*empty* directory may fail.  Ah well.)
1 parent adfacf4
Raw File
whichdb.py 
"""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 == 0x061561:
	return "dbhash"

    # Unknown
    return ""
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