7.8 Standard Module whichdb
 
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".
 
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