[Zope] When is an empty list not an empty list?

[John Schinnerer]

Aloha,

I have a python script, getCatalogItems(), which returns a (possibly 
empty) list resulting from a catalog query. The lone parameter is the 
sort index; the rest of the query is taken from the request. Anyhow...
If nothing was found, I don't want to display an empty table of results.

When I do this query and then check for empty list to see if the query 
returned any items:

<div tal:define="items python:container.getCatalogItems('id')">
<table tal:condition="python: items!=[]">
...

...it doesn not work, that is, the (empty) table displays when items is 
in fact an empty list.

If I do this instead:

<div tal:define="items python:container.getCatalogItems('id')">
<table tal:condition="python: len(items)>0">
...

...then the condition works, no empty table is displayed if the list is 
empty.

Why does the former not work and the latter does?
I need to understand the difference in the python expressions...makes no 
sense to me at present that they don't work the same.

thanks for any help,
John S.

-- 

John Schinnerer - MA, Whole Systems Design
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