A simple and slow database implemented entirely in Python. This should only be used when no other DBM-style database is available.
'r'to open an existing database for reading only,
'w'to open an existing database for reading and writing,
'c'to create the database if it doesn't exist, or
'n', which will always create a new empty database. If not specified, the default value is
The optional mode argument is the Unix mode of the file, used
only when the database has to be created. It defaults to octal
0666 (and will be modified by the prevailing umask).