On 2013-02-08 07:22, Steven D'Aprano wrote:
Rick Johnson wrote:
Why even have a damn bool function if you're never going to use it?
bool is for converting arbitrary objects into a canonical True or False
flag. E.g. one use-case is if you wish to record in permanent storage a
flag, and don't want arbitrary (possibly expensive) objects to be recorded.
Most of the time, you shouldn't care whether you have a canonical True/False
bool, you should only care whether you have something which duck-types as a
boolean flag: a truthy or falsey value. In Python, all objects duck-type as
flags. The usual interpretation is whether the object represents something
or nothing:
"nothing", or falsey values: None, False, 0, 0.0, '', [], {}, set(), etc.
(essentially, the empty value for whichever type you are considering)
"something", or truthy values: True, 1, 2.5, 'hello world', etc.
(essentially, non-empty values).
Anything that's not falsey is truey.
Prior to Python 3, the special method __bool__ was spelled __nonempty__,
which demonstrates Python's philosophy towards duck-typing bools.
Incorrect, it was spelled __nonzero__.
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