Andrew Berg wrote: > On 2011.07.07 08:39 AM, Phlip wrote: >> On Jul 7, 6:24 am, Andrew Berg <bahamutzero8...@gmail.com> wrote: >> > On 2011.07.07 08:11 AM, Phlip wrote:> No, I was pointing out that >> > passing a type is more ... typesafe. >> > >> > None is a type. >> >> I never said it wasn't.
Unfortunately, it isn't. None is not a type, it is an instance. >>> isinstance(None, type) # is None a type? False >>> isinstance(None, type(None)) # is None an instance of None's type? True So None is not itself a type, although it *has* a type: >>> type(None) <type 'NoneType'> >>> isinstance(type(None), type) # is NoneType itself a type? True > You are talking about this code, right? > > def file_to_hash(path, m=None): > if m is None: > m = hashlib.md5() > > What's not a type? The is operator compares types (m's value isn't the > only thing compared here; even an separate instance of the exact same > type would make it return False), and m can't be undefined. The is operator does not compare types, it compares instances for identity. There is no need for is to ever care about the type of the arguments -- that's just a waste of time, since a fast identity (memory location) test is sufficient. This is why I initially thought that Phlip was joking when he suggested that "m is None" could be type-unsafe. It doesn't matter what type m has, "m is <anything>" will always be perfectly safe. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
