persistent deque

[inhahe]

"castironpi" <castironpi at gmail.com> wrote in message 
news:29451c2a-cb0a-43a6-b140-6c16e3cb46ac at c65g2000hsa.googlegroups.com...
> I'd like a persistent deque, such that the instance operations all
> commit atomicly to file system.

ok, i made your persistent deque.  but there are two important notes 
regarding this module:  1) I am a genius.  2) it doesn't actually work for 
some reason.  i.e., loading an instance from file won't work.  i don't know 
why.  the pickle module is doing something i didn't expect.


from collections import deque
import os, pickle, random

class pdeque(deque):
  def __init__(self, filename, initial):
    deque.__init__(self, initial)
    self.filename = filename
    self.tempfilename = ''.join((random.choice("abcdefghijklmnopqrstuvwxyz") 
for x in xrange(10)))+".tmp"
    self.save()
  def save(self):
    pickle.dump(self, open(self.tempfilename,'wb'))
    try: os.remove(self.filename)
    except: pass
    os.rename(self.tempfilename, self.filename)
  @classmethod
  def load(cls, filename):
    return pickle.load(open(filename,'rb'))

for name in "append appendleft extend extendleft remove rotate".split():
  func = getattr(deque, name)
  def func2(instance, arg, func=func):
    result = func(instance, arg)
    instance.save()
    return result
  setattr(pdeque, name, func2)

for name in ("pop", "popleft", "clear"):
  func = getattr(deque, name)
  def func2(instance, func=func):
    result = func(instance)
    instance.save()
    return result
  setattr(pdeque, name, func2)


---

you use it just like a deque object except that when initializing the first 
parameter is a filename for it to store in.   to load the deque object again 
later, call .load(filename) on the pdeque class or a pdeque object (except 
that it doesn't work.)

i'm sure somebody here knows what obscure feature of pickling it is that's 
doing this counterintuitively.  (disclaimer: i've never used pickle to store 
a custom type before)