[Freeipa-devel] [PATCH 424] install: Introduce installer framework ipapython.install

[Jan Cholasta]

Dne 20.4.2015 v 15:14 Martin Basti napsal(a):
> On 17/04/15 16:15, Jan Cholasta wrote:
>> Dne 16.4.2015 v 16:46 Jan Cholasta napsal(a):
>>> Hi,
>>>
>>> the attached patch adds the basics of the new installer framework.
>>>
>>> As a next step, I plan to convert the install scripts to use the
>>> framework with their old code (the old code will be gradually ported to
>>> the framework later).
>>>
>>> (Note I didn't manage to write docstrings today, expect update
>>> tomorrow.)
>>
>> Added some docstrings.
>>
>> Also updated the patch to reflect little brainstorming David and I had
>> this morning.
>>
>>>
>>> Honza
>>
>>
>>
> Hello, see comments bellow:
>
> 1) We started using new shorter License header in files:
> #
> # Copyright (C) 2015  FreeIPA Contributors see COPYING for license
> #

OK.

>
> 2) IMO this will not work, NoneType has no 'obj' attribute
> +        else:
> +            if isinstance(value, from_):
> +                value = None
> +                stack.append(value.obj)
> +                continue

Right.

>
> 3) Multiple inheritance. I do not like it much.
> +class CompositeInstaller(Installer, CompositeConfigurator):

I guess you are antagonistic to multiple inheritance because of how 
other languages (like C++) do it. In Python it can be pretty elegant and 
is basis for e.g. the mixin design pattern.

>
> Installer and CompositeConfigurator inherites from Configurator class,
> and all of them implements _generator method.

Both of them call super()._generator(), so it's no problem (same for 
other methods).

>
> If I understand correctly
> (https://www.python.org/download/releases/2.3/mro/) the
> Installer._generator method will be used in this case.
> However in case when CompositeConfigurator has more levels (respectively
> it is more specialized) of inheritance, it could take precedence and its
> _generator method may be used instead.

The order of precedence is defined by the order of base classes in the 
class definition.

>
> I'm afraid this may suddenly stop working.
> Maybe I'm wrong, please fix me.

As long as you call the super class, it will work fine.

>
> And Multiple inheritance is not easily readable, this is even a diamond
> inheritance model.

Cooperative inheritance is used by design and IMHO is easily readable if 
you know how to read it. Every class defines a single bit of behavior. 
Without cooperative inheritance, it would have to be hardcoded and/or 
hacked around, which I wanted to avoid.

This blog post explains it nicely: 
<https://rhettinger.wordpress.com/2011/05/26/super-considered-super/>.

>
> --
> Martin Basti
>

-- 
Jan Cholasta