[Zope3-dev] Offtopic: soft imports

[Jim Fulton]

Florent Guillaume wrote:
> Jim wrote:
> 
>>Stephan Richter wrote:
>>
>>>Yes, I was about to suggest the same:
>>>
>>>try:
>>>  from zope.i18nmessageid import MessageIdFactory
>>>  _ = MessageIdFactory('domain')
>>>except ImportError:
>>>  _ = unicode
>>>
>>>This way you only have a soft dependence of zope.i18nmessageid
>>
>>This pattern is a bug magnet.  It has been employed before
>>do deal with this situation (message ids) specifically and has
>>caused me a world of pain.
> 
> 
> I've been bitten by that pattern a lot too, nowadays I recommend:
> 
> try:
>     from zope.i18nmessageid import MessageIdFactory
> except ImportError, e:
>     if str(e) != "No module named zope.i18nmessageid": raise
>     _ = unicode
> else:
>     _ = MessageIdFactory('domain')
> 
> But it's a bit more verbose... Anybody using this ?

I've used a variation that's less brittle:

   if 'i18nmessageid' not in str(e): ...

It really sucks that Python so often raises exceptions
with preformatted messages. You shouldn't have to screen-scrape
an exception to get it's data. :(

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