persistant dictionaries and lists for python
This is ideal for lists or dictionaries which either need persistence, are too big to fit in memory or both.
There are existing alternatives like shelve
, which are very good too.
There main difference with pysos
is that:
- the data is stored in plain text format
- it provides both persistent dicts and lists
- objects must be json "dumpable" (no cyclic references, etc.)
- it's fast (much faster than
shelve
on windows, but slightly slower than nativedbms
on linux) - it's unbuffered by design: when the function returns, you are sure it has been written on disk
- it's safe: even if the machine crashes in the middle of a big write, data will not be corrupted
- it is platform independent, unlike
shelve
which relies on an underlyingdbm
implementation, which may vary from system to system
pip install pysos
Dictionaries:
import pysos
db = pysos.Dict('somefile')
db['hello'] = 'persistence!'
Lists:
import pysos
db = pysos.List('somefile')
db.append('it is now saved in the file')
No. It's not thread safe. In practice, synchronization mechanisms are typically desired on a higher level.
In the original version, there was a switch to choose between sync and async mode. However, it turned out to have only a relatively small impact on overall performance. Less than 25% on the hardware/OS/data I tested if I remember right. Since the benefits seem rather low, I removed the flag and the associated code altogether, in order to ensure safety by default. IMHO, it's preferable to loose a few microseconds rather than data upon a crash.
I experimented with that too. In my experience, with the hardware/OS/data I tested, it turned out to ...suck. Using memory mapped files lead to inconsistent and unpredictible performance, often much slower than direct file access.