[Tutor] Another assert() question

[Martin Walsh]

Dick Moores wrote:
> At 11:44 AM 7/13/2008, Steve Willoughby wrote:
>> Dick Moores wrote:
>>> Yes! A rule, not logic. I'm not contradicting Kent, just helping
>>> myself understand. First the rule, then logic in the application of
>>> the rule. And I assume the rule is there in Python because it makes
>>> things work better.
>>
>> Yes, so a statement like "if foo:" becomes an idiom for "if the
>> collection foo has stuff in it:" which is handy whether foo is a text
>> string or a list of objects.
> 
> Yes, I've been using that, a bit uneasily.
> 
> One question about the data I listed. Why is bool(set([])) false,
> whereas bool([[]]) is true?

In the first example you're passing an empty list to the set
constructor, and getting back an empty set object. In the second, you're
providing a list with one element, which just so happens to be an empty
list, but it doesn't matter -- since the outer list is not empty.
Perhaps a better comparison would be bool(list([])) => False.

HTH,
Marty