[PEAK] Exceptions in lazy imported module not reported

[Phillip J. Eby]

At 08:23 AM 12/23/2006 -0800, Vinj Vinj wrote:
>     reload(module)
>ImportError: No module named PriceDB
>------------------------
>
>This is usually caused by an exception which is raised
>in PriceDB (in the csae above) but the error that gets
>reported by the Lazy Importing modile is: "No module
>named PriceDB"
>
>I use Lazy Importing extensively and most of my
>modules are loaded through it. The startup time of my
>app has come down significantly. However, since I'm
>running a distributed app where multiple services get
>run on different servers, when I get this error, it is
>hard to debug.
>
>Is there any way that this error can get reported.

Not that I know of.  Although in my experience, the real problem is usually 
that the error is in a module that 'PriceDB' (or whatever) is importing, 
not in PriceDB itself.  I think that this is a side-effect of the "import 
rollback" support that was added in Python 2.4, and I don't know of any way 
to work around it.


>Nice to have feature:
>The autocomplete functionality does not work with
>IDE's like WINGIDE when you lazy import. It would be
>nice to have a script (which given a list of modules)
>will replace all occurances of those modules with Lazy
>Import loads or replace them back with regular loads.

You might have more luck by implementing a PEP 302 importer object that 
takes a list of module names that should be lazy, and adding it to 
sys.meta_path.  Then, *any* import of that module would be lazy.  Something 
like:

class LazyImporter:
     def __init__(self, names):
         self.names = dict.fromkeys(names)
     def find_module(self, fullname, path=None):
         if fullname in self.names:
             return self
     def load_module(self, fullname):
         self.names.pop(fullname)
         return lazyModule(fullname)

sys.meta_path.append(
     LazyImporter(
         ['pkg1.module1', 'pkg1.module2', ....]
     )
)

I'll probably add LazyImporter to a future version of Importing, but a 
quick bit of experimenting shows that the above works nicely, e.g.:

    >>> sys.meta_path.append(LazyImporter(['email']))
    >>> import email
    >>> type(email)
    <class 'peak.util.imports.LazyModule'>

Actually accessing attributes of the 'email' package then causes it to be 
loaded for real.

Unfortunately, you can't easily extend this approach to use wildcards.