What way is the best to check an empty list?

Stef Mientki stef.mientki at gmail.com
Wed Mar 25 21:29:45 CET 2009

andrew cooke wrote:
> Andre Engels wrote:
>> On Wed, Mar 25, 2009 at 4:21 PM, andrew cooke <andrew at acooke.org> wrote:
>>> i will go against the grain slightly and say that "len" is probably the
>>> best compromise in most situations (although i admit i don't know what
> [...]
>>> but i may be wrong - are there any containers (apart from pathological
>>> hand-crafted examples) that would not define __len__()?
>> When writing my answer, I thought of generators, but I now find that
>> those will have boolean value 'true' whether or not they have
>> something to generate, so they will go wrong under either method. The
>> same holds for iterators. So for now I can't find any good example.
> actually, the implication of what you said is probably worth emphasising
> to the original poster: often you don't need to test whether a list is
> empty or not, you simply iterate over its contents:
>   for x in foo:
>     # do something
> this will then work with lists, tuples, sets, but also with iterators and
> generators (which would give incorrect results in a test).  in all cases,
> "do something" will not happen if there are no data to process.
Now it would be nice to allow iteration over others too, like None .
    a = None
    for item in a :

I created a Null object for that, but that gives all kind of problems 
with i.e. configobj.

> andrew
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