# 7.11 `whichdb` -- Guess which DBM module created a database

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`(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'`.