11.7. "whichdb" — Guess which DBM module created a database
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Note: The "whichdb" module’s only function has been put into the
  "dbm" module in Python 3.  The *2to3* tool will automatically adapt
  imports when converting your sources to Python 3.

The single function in this module attempts to guess which of the
several simple database modules available—"dbm", "gdbm", or
"dbhash"—should be used to open a given file.

whichdb.whichdb(filename)

   Returns one of the following values: "None" if the file can’t be
   opened because it’s unreadable or doesn’t exist; the empty string
   ("''") if the file’s format can’t be guessed; or a string
   containing the required module name, such as "'dbm'" or "'gdbm'".