[Zope3-Users] Using 'if object' evaluates false even if objectexists

[Giovannetti, Mark]

Hi Aleksander,

Thanks for your response.  And thanks to Benji, too, for 
replying with the informative link.  More below...

> From zope3-users On Behalf Of Aleksander Kowalczyk
> 
> On 4/12/07, Giovannetti, Mark <giovanne at nrcan.gc.ca> wrote:
> 
> 	Hi list,
> 	
> 	Hope everyone's having a splendid day/evening/whatever.
> 	
> 	I've encountered a strange error.  I have two chunks
> 	of nearly identical code below.  The only difference
> 	is the first "if" statement.  One has: 
> 	
> 	    if context:
> 	
> 	the other has:
> 	
> 	    if context is not None
> 	
> 	The first fails to be true even if context is not None.
> 	This can be seen by the output from the logs showing the
> 	context variable as: 
> 
> Possibly a context is a container-like object.
> For containers operation
> "if context" is equal to "if len(context) > 0".  So even if 
> context is not None, it still may be False if the container 
> does not contain any elements. 
> 

This occurred to me at about the same time I read your message.
The context is indeed a container (which happened to be empty),
thus the false evaluation as you suggest.

Another nugget of useful python/zope programming knowledge!

Regards
Mark