On Thu, Jan 8, 2009 at 5:53 AM, Sergey Kishchenko <void...@gmail.com> wrote: > In Python empty container equals False in 'if' statements: > > # prints "It's ok" > if not []: > print "It's ok" > > Let's create a simple Foo class: > > class Foo: > pass > > Now I can use Foo objects in 'if' statements: > > #prints "Ouch!" > f=Foo() > if f: > print "Ouch!" > > So, default __nonzero__ impl is to return True. I think, this > behaviour conflicts with 'Explicit is better than implicit' and > 'Practicality beats purity' statements. I think, throwing a TypeError > exception would be better. It will result in more explicit code with > fewer errors.
Python has a rich notion of boolean truth compared to other languages. In this case, by default, non-None objects are considered True. It's a reasonable default behavior since wanting to differentiate between None and non-None objects is such a common task. Also, I've been programming in Python for a long while and have yet to encounter any bug due to this behavior. Regarding the Zen, on the contrary, this is a perfect example of "Practicality beats purity" in action. Cheers, Chris -- Follow the path of the Iguana... http://rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
