""" Implementation of the PostgreSQL backend for sessions. It assumes

a table like this::

create table session (

id varchar(40),

data text,

expiration_time timestamp

)

You must provide your own get_db function.

"""

pickle_protocol = pickle.HIGHEST_PROTOCOL

def __init__(self, id=None, **kwargs):

Session.__init__(self, id, **kwargs)

self.locks={}

@classmethod

def setup(cls, **kwargs):

"""Set up the storage system for Postgres-based sessions.

This should only be called once per process; this will be done

automatically when using sessions.init (as the built-in Tool does).

"""

for k, v in kwargs.items():

setattr(cls, k, v)

cls.locks={}

def cls__del__(self):

pass

def _exists(self):

# Select session data from table

with connect() as db:

cursor=db.cursor()

cursor.execute('select data, expiration_time from session '

'where id=%s', (self.id,))

rows = cursor.fetchall()

return bool(rows)

def _load(self):

# Select session data from table

with connect() as db:

cursor=db.cursor()

cursor.execute('select data, expiration_time from session '

'where id=%s', (self.id,))

rows = cursor.fetchall()

if not rows:

return None

pickled_data, expiration_time = rows[0]

data = pickle.loads(pickled_data)

return data, expiration_time

def _save(self, expiration_time):

pickled_data = pickle.dumps(self._data, self.pickle_protocol)

with connect() as db:

db.cursor().execute('replace into session (data,expiration_time,id) values (%s,%s,%s)',

(pickled_data, expiration_time, self.id))

db.commit()

def _delete(self):

with connect() as db:

db.cursor().execute('delete from session where id=%s', (self.id,))

db.commit()

def acquire_lock(self):

"""Acquire an exclusive lock on the currently-loaded session data."""

self.locked = True

self.locks.setdefault(self.id, threading.RLock()).acquire()

def release_lock(self):

"""Release the lock on the currently-loaded session data."""

self.locks[self.id].release()

self.locked = False

def clean_up(self):

"""Clean up expired sessions."""

with connect() as db:

db.cursor().execute('delete from session where expiration_time < %s',

(self.now(),))

db.commit()