On Fri, Jul 28, 2017 at 10:09 AM, Mike Miller <python-ideas@mgmiller.net> wrote:
I've never liked that error message either:
>>> object().foo = 'bar' Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'object' object has no attribute 'foo'
Should say the "object is immutable," not writable, or something of the sort.
As Ivan said, this is to do with __slots__. It's nothing to do with immutability:
class Demo: ... __slots__ = 'spam' ... x = Demo() x.spam = 1 x.ham = 2 Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'Demo' object has no attribute 'ham'
If the object has a __dict__, any unknown attributes go into there:
class Demo2(Demo): pass ... y = Demo2() y.ham = 2 y.spam = 3 y.__dict__ {'ham': 2}
which prevents that "has no attribute" error. ChrisA