[Zope3-Users] Re: Problem with interdependent utilities registration

[Philipp von Weitershausen]

Yuan HOng wrote:
> If I have a utility component whose initializaiton depends on the
> availability of another utility, the initialization fails with a
> Component Lookup Error. It seems that in the ZCML file, the utility
> components are first created, and then at the end of the whole
> configuration, they are registered.

Yup.

> So if in the initilization code of utility B I need to look up a
> utility A, the ZCML configuration will  fail.

That's why you shouldn't look up any components in __init__ :)

> The problem is that although the z3c eninge object is created before
> the 'utility' directive is executed, it is not registered and
> therefore can not be looked up when the 'utility' directive tries to
> create the MyUtility object.
> 
> How does one usually solve such interdependencies?

Look up the utility when you actually *need* it. This is a general rule 
of thumb, because you always want to preserve the possibility of local 
utilities coming from some local sites, and those aren't available 
during some initialization code.