a couple of questions: pickling objects and strict types

[Steven D'Aprano]

On Fri, 05 Apr 2013 18:18:51 -0600, Littlefield, Tyler wrote:

> On 4/5/2013 2:30 PM, Steven D'Aprano wrote:
>> On Fri, 05 Apr 2013 12:59:04 -0600, Littlefield, Tyler wrote:
>>
>>> Hello all:
>>> I've been using Python for a while now, but I have one larger problem.
>>> I come from a c++ background; though it doesn't help in catching
>>> runtime errors, being able to compile a program helps catch a lot of
>>> syntax errors. I know about pychecker, which is somewhat useful. Do
>>> people have other methods for handling this?
>>
>> Do you tend to make a lot of syntax errors?
>
> Not a -lot-, but there are things I don't catch sometimes.

As we all do. But fortunately the Python compiler catches syntax errors.


>> Python also catches syntax errors at compile-time. I won't speak for
>> others, but I hardly ever make syntax errors: between Python's simple,
>> surprise-free syntax, and modern, syntax-colouring editors, I find that
>> I rarely make syntax errors.
> 
> I am blind, so colorful editors don't really work all that well for me.

Fair point.


>>> Also, I'm depickling objects. Is there a way I can force pickle to
>>> call the object's ctor? I set up events per object, but when it just
>>> deserializes it doesn't set all that up. Thanks,
>> What's the object's ctor? What sort of objects are you dealing with?
>>
>>
>>
>      def __init__(self):
>          self.events = {}
>          self.components = []
>          self.contents = []
>          self.uid = uuid4().int
>          self.events['OnLook'] = teventlet()
> 
> 
> Basically events don't get initialized like I'd like after I depickle
> objects.

Did you mean "constructor" rather than C T O R ? Perhaps your voice-to-
text software (if you are using such) misheard you.

Correct, by default pickle does not call the __init__ method, it just 
reconstructs the instance. Basically, it takes a snapshot of the 
instance's internal state (the __dict__) and reconstructs from the 
snapshot.

This is explained in the documentation here:

http://docs.python.org/2/library/pickle.html#the-pickle-protocol


You can force the __init__ method to be called in a couple of different 
ways. Perhaps this is the most straight-forward. Add a __setstate__ 
method to your class:


    def __setstate__(self, state):
        self.__dict__.update(state)
        self.events['OnLook'] = teventlet()



-- 
Steven