[FRPythoneers] looking for help with elementtree

Sean Gillies sgillies at frii.com
Sat Jun 28 07:39:16 MDT 2003


On Friday, June 27, 2003, at 09:13  PM, Tom Hall wrote:

> On Fri, Jun 27, 2003 at 06:59:02PM -0600, Sean Gillies wrote:
>> Nevermind ... found the problem.
>
> Well, what was it !
>

I'm looking for a sub-element tagged 'ENVELOPE' within a
'PROPERTIES' element, so I do:

   envelope = properties.find('ENVELOPE')

Then I write code to go on and do something with this new
element after testing that it's been found:

   if envelope:
     # process

envelope doesn't seem to evaluate to true as it should.
Rewritten as

   if envelope is not None:
     # process

my code executes as intended.  According to 5.10 of the reference
manual:

"""
In the context of Boolean operations, and also when expressions are 
used by control flow statements, the following values are interpreted 
as false: None, numeric zero of all types, empty sequences (strings, 
tuples and lists), and empty mappings (dictionaries). All other values 
are interpreted as true.
"""

In my case, envelope has no child elements, so perhaps it is being
evaluated as an empty sequence in the 'if' context?

Overall, I'm finding elementtree extremely handy for dealing with
small XML documents.

S.

--
Sean Gillies
sgillies at frii dot com
http://www.frii.com/~sgillies




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