[Product-Developers] Re: unit test on Plone 4.0b1

[Martin Aspeli]

Ross Patterson wrote:
> Derek Broughton<derek at pointerstop.ca>  writes:
>
>> Wichert Akkerman wrote:
>>
>>> On 3/20/10 15:33 , Derek Broughton wrote:
>>>> Thanks for this discussion - I'm loathe to even test Plone4 at the
>>>> moment beccause I don't know enough about this sort of change.
>>>>
>>>> Surely, though, dependencies on something like CMFCore should be
>>>> fulfilled by declaring the dependency on Plone.
>>> They are, but you should never rely on that: Plone might be modified
>>> to not use CMFCore anymore itself, and your package would suddenly
>>> break.  For Plone and CMFCore that is not very likely short term, but
>>> in general you should never rely on indirect dependencies. They
>>> *will* hurt you at some point.
>> Ah, but I rather look at it the opposite way - I _should_ rely on
>> indirect dependencies for something like CMFCore, because I only use
>> it as required in Plone.  If plone was to drop that dependency and use
>> something else (specifically this _did_ happen with CMFCore
>> Permissions - at least the module moved), I _want_ my product to break
>> and require me to fix my code.  The absolutely last thing I want is
>> for my code to continue to import something that will only be used by
>> my own products while everybody else is doing something different.
>
> +1  Well said, I've often thought this when I've heard the
> above install_requires dogma.

I think the rule of thumb is pretty easy:

  - if you import from a package in your own code, declare a dependency 
on it

So, if you use 'from Products.CMFCore.utils import getToolByName', then 
declare a dependency on 'Products.CMFCore'. If that package disappeared 
from the dependency tree, your code would break.

If you don't import anything from Products.Archetypes or whatever, then 
don't declare a dependency on it.

Sometimes, 'import from' can also mean 'use a ZPT macro in' or similar.

Martin

-- 
Author of `Professional Plone Development`, a book for developers who
want to work with Plone. See http://martinaspeli.net/plone-book