[Python-Dev] Circular imports considered harmful (was import.c)

[Jim Fulton]

Tim Peters wrote:
> Does anyone living understand import.c in all its gory glory now?
> 

...

> 2. Zope3 in particular is having horrid problems with circular
>    imports.  These are also a bitch to track down.  I'm not sure
>    it was any better in Zope2, but Zope3 has been undergoing
>    frequent and massive refactorings (and a new round of unintended
>    circular imports creates subtle problems each time).

I wouldn't put it quite that dramatically, but it's bad enough
that I've asked Fred to put together a tool to detect circular
imports as part of our testing framework.  The problems with circular
imports, at least in a large system like Zope 3, are:

- They often work

- Whether or not they work can depend on the order
   that you import seemingly unrelated modules.

- Often, by the time they fail, you've unwittingly created a rat's
   nest that's a pain to untangle.

I think just having a tool to easily detect them will be a major step
forward.

Jim

-- 
Jim Fulton           mailto:jim at zope.com       Python Powered!
CTO                  (540) 361-1714            http://www.python.org
Zope Corporation     http://www.zope.com       http://www.zope.org