On 5/8/2011 10:07 AM, Steven D'Aprano wrote:
Because the test of "is this nothing, or something?" is a common, useful test:
Because inductive algorithms commonly branch on 'input is something' (not done, change args toward 'nothing'and recurse or iterate) versus 'input is nothing (done, return base expression).
0 (nothing) vs 1, 2, 3, ... (something) empty list versus non-empty list empty dict versus non-empty dict empty set versus non-empty set empty string versus non-empty string
and non-inductive algorithms also branch on the same question.
no search results returned versus some search results returned no network connection available versus some network connection available no food in the cupboard versus food in the cupboard This is a fundamental distinction which is very useful in practice.
Definitely. Python commonly hides the distinction inside of iterators called by for statememts, but StopIteration is understood as 'collection is empty'. An I suspect something vs. nothing is also the most common overt condition in if and while statements.
-- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
