Need advice on python importing

[Matthew Wilson]

On Fri 17 Oct 2008 04:52:47 PM EDT, Steve Holden wrote:
> Matthew Wilson wrote:
>> I started with a module with a bunch of classes that represent database
>> tables.  A lot of these classes have methods that use other classes
>> inside, sort of like this:
>> 
>>     class C(object):
>>         @classmethod
>>         def c1(cls, a):
>>             return a
>> 
>>     class D(object):
>>         def d1(self, a):
>>             return a + C.c1(a)
>> 
>> Notice how the d1 method on class D uses a classmethod c1 on C.  C is in
>> the same module, so it's globally available.
>> 
>> I moved my classes C and D into different files, and then I noticed that
>> D now needed to import C first.  That worked fine until I wrote
>> interdependent classes that couldn't import each other.
>> 
>> So I passed in everything as parameters like this:
>> 
>>     def d1(self, C, a):
>>     
>> That works fine, but now I've got some methods that have six
>> parameters (or more) that are entirely just for this purpose.  So, now
>> instead of passing these in as parameters, I'm passing them into my
>> initializer and binding them in to self.
>> 
>> I wanted to use functools.partial to bind on these parameters like this:
>> 
>>     d1 = functools.partial(d1, C=C)
>> 
>> But partial objects don't get the self parameter passed in, so using
>> partial is is effectively similar to decorating methods with
>> staticmethod.  Here's a link to the documentation on partial that
>> explains this:
>> 
>>     http://www.python.org/doc/2.5.2/lib/partial-objects.html
>> 
>> So, partials won't work.
>> 
>> I suspect that there's more elegant solutions for this.
>> 
>> All thoughts are welcome.
>
> Explain why you are using classmethods instead of regular methods in the
> first case (I appreciate your actual code will be rather more complex
> than your examples).

Hi Steve, I'm using SQLObject classes, and joining one table with
another requires either the class or an instance for the class.  So, I
could pass in instances of all the classes, and I'd be at the same
point.  I just don't like seeing functions with lots and lots of
parameters.

Thanks for the feedback!