On Thursday 23 June 2016 14:47, Lawrence D’Oliveiro wrote: > On Thursday, June 23, 2016 at 3:12:52 PM UTC+12, Larry Hudson wrote: >> On 06/22/2016 12:42 AM, Lawrence D’Oliveiro wrote: >>> * boolean operators don’t have to operate on boolean values. The >>> language spec >>> <https://docs.python.org/3/reference/expressions.html#boolean-operations> >>> says: >>> >>> “...the following values are interpreted as false: False, None, numeric >>> zero of all types, and empty strings and containers (including strings, >>> tuples, lists, dictionaries, sets and frozensets). All other values are >>> interpreted as true.” >>> >>> I feel that’s a needlessly complicated rule.
As I described in my earlier email, it isn't complicated, at least not the way builtins are modelled. >>> It would have been simpler if >>> boolean operators (and conditional expressions like in if-statements and >>> while-statements) only allowed values of boolean types. But that’s one of >>> the few warts in the design of Python... >> >> Wart?? I *strongly* disagree. I find it one of the strengths of Python, >> it enhances Python's expressiveness. > > Tightening it up would rule out a whole class of common errors, Hardly common. The only two exceptions I've seen are: - people surprised by midnight being false, but that is fixed in 3.5; - people surprised that empty or exhausted iterables don't evaluate as false and the first of those is pretty rare. But even if you were right, and I disagree that you are, "fixing" this would break backwards compatibility and cause vast amounts of working code to stop working. That is much worse than the "problem". > from > misunderstanding (or forgetting) the rule about what exactly gets interpreted > as true and what as false <https://bugs.python.org/issue13936> > <http://stackoverflow.com/questions/28116931/datetime-time0-0-evaluates-as- false-in-boolean-context>. Or... we could fix time objects, as was done. -- Steve -- https://mail.python.org/mailman/listinfo/python-list
