>>> from tiramisu.option import (StrOption,
OptionDescription, Config,
default_storage, Storage)
>>> default_storage.settings(engine='sqlite3', dir_database='/tmp/tiramisu')
>>> s = StrOption('str', '')
>>> o = OptionDescription('od', '', [s])
>>> c1 = Config(o, persistent=True, session_id='session')
>>> print(c1.option('str').value.get())
>>> c1.option('str').value.set('yes')
>>> print(c1.option('str').value.get())
'yes'
>>> del(c1)
>>> c2 = Config(o, persistent=True, session_id='session')
>>> print(c2.option('str').value.get())
'yes'
>>> del(c2)
>>> list_sessions()
['session']
>>> delete_session('xxxx')
>>> c3 = Config(o, persistent=True, session_id='session')
>>> print(c3.option('str').value.get())
