text: """Generic interface to all dbm clones.
  
  Use
  
          import dbm
          d = dbm.open(file, 'w', 0o666)
  
  The returned object is a dbm.bsd, dbm.gnu, dbm.ndbm or dbm.dumb
  object, dependent on the type of database being opened (determined by
  the whichdb function) in the case of an existing dbm.  If the dbm does
  not exist and the create or new flag ('c' or 'n') was specified, the
  dbm type will be determined by the availability of the modules (tested
  in the above order).
  
  It has the following interface (key and data are strings):
  
          d[key] = data   # store data at key (may override data at
                          # existing key)
          data = d[key]   # retrieve data at key (raise KeyError if no
                          # such key)
          del d[key]      # delete data stored at key (raises KeyError
                          # if no such key)
          flag = key in d # true if the key exists
          list = d.keys() # return a list of all existing keys (slow!)
  
  Future versions may change the order in which implementations are
  tested for existence, and add interfaces to other dbm-like
  implementations.
  """
  
  __all__ = ['open', 'whichdb', 'error', 'error']
  
  import io
  import os
  import struct
  import sys
  
  
  class error(Exception):
      pass
  
  _names = ['dbm.bsd', 'dbm.gnu', 'dbm.ndbm', 'dbm.dumb']
  _defaultmod = None
  _modules = {}
  
  error = (error, IOError)
  
  
  def open(file, flag='r', mode=0o666):
      """Open or create database at path given by *file*.
  
      Optional argument *flag* can be 'r' (default) for read-only access, 'w'
      for read-write access of an existing database, 'c' for read-write access
      to a new or existing database, and 'n' for read-write access to a new
      database.
  
      Note: 'r' and 'w' fail if the database doesn't exist; 'c' creates it
      only if it doesn't exist; and 'n' always creates a new database.
      """
      global _defaultmod
      if _defaultmod is None:
          for name in _names:
              try:
                  mod = __import__(name, fromlist=['open'])
              except ImportError:
                  continue
              if not _defaultmod:
                  _defaultmod = mod
              _modules[name] = mod
          if not _defaultmod:
              raise ImportError("no dbm clone found; tried %s" % _names)
  
      # guess the type of an existing database, if not creating a new one
      result = whichdb(file) if 'n' not in flag else None
      if result is None:
          # db doesn't exist or 'n' flag was specified to create a new db
          if 'c' in flag or 'n' in flag:
              # file doesn't exist and the new flag was used so use default type
              mod = _defaultmod
          else:
              raise error[0]("need 'c' or 'n' flag to open new db")
      elif result == "":
          # db type cannot be determined
          raise error[0]("db type could not be determined")
      elif result not in _modules:
          raise error[0]("db type is {0}, but the module is not "
                         "available".format(result))
      else:
          mod = _modules[result]
      return mod.open(file, flag, mode)
  
  
  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 name of the dbm submodule (e.g. "ndbm" or "gnu") if recognized.
  
      Importing the given module may still fail, and opening the
      database using that module may still fail.
      """
  
      # Check for ndbm first -- this has a .pag and a .dir file
      try:
          f = io.open(filename + ".pag", "rb")
          f.close()
          # dbm linked with gdbm on OS/2 doesn't have .dir file
          if not (ndbm.library == "GNU gdbm" and sys.platform == "os2emx"):
              f = io.open(filename + ".dir", "rb")
              f.close()
          return "dbm.ndbm"
      except IOError:
          # some dbm emulations based on Berkeley DB generate a .db file
          # some do not, but they should be caught by the bsd checks
          try:
              f = io.open(filename + ".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 ndbm is not None:
                  d = ndbm.open(filename)
                  d.close()
                  return "dbm.ndbm"
          except IOError:
              pass
  
      # Check for dumbdbm next -- this has a .dir and a .dat file
      try:
          # First check for presence of files
          os.stat(filename + ".dat")
          size = os.stat(filename + ".dir").st_size
          # dumbdbm files with no keys are empty
          if size == 0:
              return "dbm.dumb"
          f = io.open(filename + ".dir", "rb")
          try:
              if f.read(1) in (b"'", b'"'):
                  return "dbm.dumb"
          finally:
              f.close()
      except (OSError, IOError):
          pass
  
      # See if the file exists, return None if not
      try:
          f = io.open(filename, "rb")
      except IOError:
          return None
  
      # Read the start of the file -- the magic number
      s16 = f.read(16)
      f.close()
      s = s16[0:4]
  
      # 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 "dbm.gnu"
  
      ## Check for old Berkeley db hash file format v2
      #if magic in (0x00061561, 0x61150600):
      #    return "bsddb185" # not supported anymore
  
      # Later versions of Berkeley db hash file have a 12-byte pad in
      # front of the file type
      try:
          (magic,) = struct.unpack("=l", s16[-4:])
      except struct.error:
          return ""
  
      ## Check for BSD hash
      #if magic in (0x00061561, 0x61150600):
      #    return "dbm.bsd"
  
      # Unknown
      return ""
  
  
  if __name__ == "__main__":
      for filename in sys.argv[1:]:
          print(whichdb(filename) or "UNKNOWN", filename)
  