checking if a list is empty

[Steven D'Aprano]

On Thu, 12 May 2011 23:46:12 -0700, rusi wrote:

> Mathematics has existed for millenia. Hindu-arabic numerals (base-10
> numbers) have been known for about one millennium
> The boolean domain is only a 100 years old. Unsurprisingly it is not
> quite 'first-class' yet: See
> http://www.cs.utexas.edu/users/EWD/transcriptions/EWD10xx/EWD1070.html
> [Lifted from http://c2.com/cgi/wiki?EqualVsTrueFalse ]

Th money-quote as regards using arbitrary objects in truth tests:

    [quote]
    All this changed with the introduction of the two-element 
    boolean domain {true, false} which provides the vocabulary 
    needed to assign values to boolean expressions: 3<4 is a 
    way for writing true, 3>4 is a way for writing false, 
    whereas the value of x>0 depends on the value of x ...
    [end quote]


In Python, [1, 2, 3] is another way of writing true, and [] is another 
way of writing false. Similarly with any other arbitrary objects. The 
only things that bools True and False are good for are:

* giving functions a canonical way of spelling true/false when they want 
to emit a Boolean value;

* giving documentation writers a canonical way of spelling true/false 
when they want to discuss passing a Boolean value.

Other than those conveniences, there's nothing you can do with True and 
False in Python that you can't do with any other set of objects.


-- 
Steven