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i am trying to implement my own version of a DailyLogFile 

from twisted.python.logfile import DailyLogFile class NDailyLogFile(DailyLogFile): def __init__(self, name, directory, rotateAfterN = 1, defaultMode=None): DailyLogFile.__init__(self, name, directory, defaultMode) # why do not use super. here? lisibility maybe? # self.rotateAfterN = rotateAfterN def shouldRotate(self): """Rotate when N days have passed since file creation""" delta = datetime.date(*self.toDate()) - datetime.date(*self.toDate(self.createdOn)) return delta > datetime.timedelta(self.rotateAfterN) def __getstate__(self): state = BaseLogFile.__getstate__(self) del state["rotateAfterN"] return state threadable.synchronize(NDailyLogFile)

but it looks like i miss a fundamental of Python subclassing process...as i get this error :

Traceback (most recent call last): File "/home/twistedtestproxy04.py", line 88, in <module> import ndailylogfile File "/home/ndailylogfile.py", line 56, in <module> threadable.synchronize(NDailyLogFile) File "/home/lt/mpv0/lib/python2.6/site-packages/twisted/python/threadable.py", line 71, in synchronize sync = _sync(klass, klass.__dict__[methodName]) KeyError: 'write'

so i need to explicitly add and define others methods like Write and rotate method like this:

class NDailyLogFile(DailyLogFile): [...] def write(self, data): # why must i add these ? DailyLogFile.write(self, data) def rotate(self): # as we do nothing more than calling the method from the base class! DailyLogFile.rotate(self) threadable.synchronize(NDailyLogFile)

while i thought it would be correctly inherit from the base mother class. Notice that i do nothing, only calling "super",

please can someone explain why i am wrong on my first idea that it was not necessary to add the Write method?

is there a way to say to Python inside my NDailyLogFile that it shoud have all the methods DailyLogFile that are not defined directly from its mother class? So that it prevents this king of error _sync(klass, klass.__dict__[methodName] and that avoid to specify excplicitly ?

( original code of DailyLogFile that inspired me it taken from the twisted source here https://github.com/tzuryby/freespeech/blob/master/twisted/python/logfile.py )

EDIT: about using super, i get: 

 File "/home/lt/inwork/ndailylogfile.py", line 57, in write super.write(self, data) exceptions.AttributeError: type object 'super' has no attribute 'write'

so will not use it. My thoughs was it was right... i must have definitively missed something

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    From OOP perspective you are doing it right, except you don't really want to override all the methods. And you should really use super. The problem is that threadable.py is not very friendly to that OOP stuff, as the line that throws an error checks for existence of write in that particular class, but not it's ancestors. I have no experience with twisted so don't know how to overcome this. Maybe there are some guides on that somewhere on the internet? Commented Jun 12, 2013 at 20:18
  • ok, thank you for the comment. I do not know if there is a better answer for now. but you have provide a good part :) Commented Jun 12, 2013 at 20:24
  • I think the silly and probably wrong way to achieve what are you trying to do is to replace that klass.__dict__[methodName] with getattr(klass, methodname) in threadable.py. And most likely it won't work. And it's a patch to twisted. And it probably breaks something outside that particular use case. So, please try it as a proof of concept and if it really works - suggest as a patch to twisted via ailing lists or ticket tracker or whatever they use to leverage development. And don't forget to post something here so I would know if it helped :) Commented Jun 12, 2013 at 20:38
  • well you help me a lot and should have provided an anwser so i can accept it. I'm not going to patch threadable.py and will add the define has stated in my own subclass. As it is the easiest way :) Commented Jun 12, 2013 at 20:51
  • try to set NDailyLogFile.synchronized to include only methods that you want to be overridden and to be syncrhonized i.e., don't overwrite write method. I'm assuming that parent methods remain synchronized and the lock is the same. Commented Jun 12, 2013 at 21:56

2 Answers 2

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There is one workaround, just do:

NDailyLogFile.__dict__ = dict( NDailyLogFile.__dict__.items() + DailyLogFile.__dict__.items() ) threadable.synchronize(NDailyLogFile)

There is a problem here that you are using the class without having instantiated it. This workaround works because you are forcing to change the class attributes before the instantiation.

Another important comment ist that for a subclass of DailyLogFile the command super would not work, since DailyLogFile is a so called "old style class", or "classobj". The super works for the "new style" classes only. See this question for further information about this.

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I dare say that the twisted/python/threadable.py code has a bug in it. __dict__ only returns the local attributes, not the inherited attributes. Other posts say to use dir() or inspect.getmembers() to get them.

The good news is that you are correct on your first idea that the write method is inherited. The bad news is that Twisted doesn't recognize inherited methods, so you have to write them yourself.

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dir will return a list of stuff attributes and methods, but not the methods themselves. inspect.getmembers returns a list of tuples of structure (name, value), so it's possible to find a method, but harder than just using getattr.
so i may add them explicitly from the subclass without having to define them? i am not sure to get the point here on how i could use dir or inspect.getmembers() for this.
@user2468222 you'll have to patch threadable.py anyway, but do it in a more involving way than using getattr

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