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'.
