Trouble using pinckle
in [Python]
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From: Pierre-Alain Dorange on 2 Jul 2008 10:09 Hello, I'm new to python and i'm deelopping a small game with pygame. I got lot of fun with python. Trying to implement a config file to save user score and config. Reading doc and some tutorial about file handling i read about pickle, and yes it's very easy to implement. But i thought i miss something with the roots of python. I implement a Prefs class to handle config data and add it a load and save method. It works but when reading self, it OK inside the load function but outside the pref instance return to it's previus state... I don't really understand. Here's the test code : #!/usr/bin/env python import os, pickle kFileName='test.ini' class Prefs(): def __init__(self): self.test=1 self.zorglub='bonjour' def load(self): if os.path.exists(kFileName): try: print 'test %d (before)' % self.test f=open(kFileName,'r') self=pickle.load(f) f.close() print 'test %d (after)' % self.test except IOError: return 1 return 0 def save(self): f=open(kFileName,'w') pickle.dump(self,f) f.close() return 0 def main(): p=Prefs() p.load() print 'test %d (after load)' % p.test p.test+=1 print 'test %d (before save)' % p.test p.save() print '----------------------' if __name__ == '__main__': main() -- Pierre-Alain Dorange Vid�o, DV et QuickTime <http://www.garage-video.com/> Clarus, the DogCow <http://clarus.chez.tiscali.fr/>
From: Cédric Lucantis on 2 Jul 2008 10:45 Le Wednesday 02 July 2008 16:09:07 Pierre-Alain Dorange, vous avez écrit : > Hello, > > I'm new to python and i'm deelopping a small game with pygame. > I got lot of fun with python. > > Trying to implement a config file to save user score and config. > Reading doc and some tutorial about file handling i read about pickle, > and yes it's very easy to implement. > But i thought i miss something with the roots of python. > > I implement a Prefs class to handle config data and add it a load and > save method. It works but when reading self, it OK inside the load > function but outside the pref instance return to it's previus state... > I don't really understand. > > Here's the test code : > > #!/usr/bin/env python > > import os, pickle > > kFileName='test.ini' > > class Prefs(): note that using new-style classes is recommended today: class Prefs (object) : > def __init__(self): > self.test=1 > self.zorglub='bonjour' > > def load(self): > if os.path.exists(kFileName): > try: > print 'test %d (before)' % self.test > f=open(kFileName,'r') > self=pickle.load(f) > f.close() > print 'test %d (after)' % self.test > except IOError: > return 1 > > return 0 > Here self is only a local variable and its meaning is only a convention. So assigning it to a new value won't change the object itself (and is not a good idea as it may be confusing for the reader). You should either use a static method which returns a new object: class Prefs (object) : def save (self, f) : pickle.dump(self, f) @staticmethod def load (f) : return pickle.load(f) and load it with "prefs = Prefs.load(filename)" or store all the values in a dictionary and only pickle this object: class Prefs (object) : def __init__ (self) : self.values = { 'test': 1, ... } def save (self, f) : pickle.dump(self.values, f) def load (self, f) : self.values = pickle.load(f) -- Cédric Lucantis
From: Pierre-Alain Dorange on 2 Jul 2008 11:49 C�dric Lucantis <omer(a)no-log.org> wrote: > Here self is only a local variable and its meaning is only a convention. So > assigning it to a new value won't change the object itself (and is not a good > idea as it may be confusing for the reader). Thanks, i was thinking about something like that. > You should either use a static method which returns a new object: > > class Prefs (object) : > > def save (self, f) : > pickle.dump(self, f) > > @staticmethod > def load (f) : > return pickle.load(f) > > and load it with "prefs = Prefs.load(filename)" > > or store all the values in a dictionary and only pickle this object: > > class Prefs (object) : > > def __init__ (self) : > self.values = { 'test': 1, ... } > > def save (self, f) : > pickle.dump(self.values, f) > > def load (self, f) : > self.values = pickle.load(f) I try the staticmethod, it works fine. Very helpful. But i don't like it very much, it seems 'complicated' (python was supposed to be simple). I'll also try the dictionnary method. My final idea was that a dictionnary would be perhaps simple in the future to save/load as XML and a parser. But perhaps i'm wrong with my vision of python. On a more global perspective, what are the best method to implement a simple config file with pyhton. Assuming i finally want to made a bundle app for Mac, Windows and perhaps Linux. I develop on Mac, and on this platform the config fil (preferences) have to be stored in a special directory : ~/Library/Preferences, no problem. But on other platform that's not the same directory and perhaps i would also faced to permissions issues... But first is there a way to determine on which platfrom the python script is running ? -- Pierre-Alain Dorange Vid�o, DV et QuickTime <http://www.garage-video.com/> Clarus, the DogCow <http://clarus.chez.tiscali.fr/>
From: Bruno Desthuilliers on 2 Jul 2008 12:11 Pierre-Alain Dorange a �crit : > C�dric Lucantis <omer(a)no-log.org> wrote: > >> Here self is only a local variable and its meaning is only a convention. So >> assigning it to a new value won't change the object itself (and is not a good >> idea as it may be confusing for the reader). > > Thanks, i was thinking about something like that. > (snip) > I try the staticmethod, it works fine. Very helpful. > > But i don't like it very much, it seems 'complicated' (python was > supposed to be simple). Try doing the same thing in C++ !-) > I'll also try the dictionnary method. > My final idea was that a dictionnary would be perhaps simple in the > future to save/load as XML and a parser. XML ? What a strange idea ? > But perhaps i'm wrong with my vision of python. > > On a more global perspective, what are the best method to implement a > simple config file with pyhton. Well... Python does have a couple of config-related packages, starting with the one in the stdlib. You may want to find out if any of these packages fits your needs before reinventing the wheel ? > Assuming i finally want to made a bundle > app for Mac, Windows and perhaps Linux. > I develop on Mac, and on this platform the config fil (preferences) have > to be stored in a special directory : ~/Library/Preferences, no problem. > But on other platform that's not the same directory and perhaps i would > also faced to permissions issues... Yeps. Portability sometimes has a cost. I can't help you wrt/ Windows, but on unix the convention is to save user's prefs in a .yourprogram file (or directory) in the user's home directory. > But first is there a way to determine on which platfrom the python > script is running ? the os package is your friend.
From: Cédric Lucantis on 2 Jul 2008 12:40
> > I'll also try the dictionnary method. > > My final idea was that a dictionnary would be perhaps simple in the > > future to save/load as XML and a parser. > XML ? What a strange idea ? Why is it so strange ? Many softs have their config in xml, and the xml.* modules are not that hard to use. It makes sense if you have a lot of config entries with nested sections. > > On a more global perspective, what are the best method to implement a > > simple config file with pyhton. > > Well... Python does have a couple of config-related packages, starting > with the one in the stdlib. You may want to find out if any of these > packages fits your needs before reinventing the wheel ? Right, ConfigParser should do the trick for simpler things. -- Cédric Lucantis |