On 24/01/2015 20:24, Terry Reedy wrote:
On 1/24/2015 5:16 AM, Mario Figueiredo wrote:
Consider the following code at your REPL of choice
class Sub:
pass
foo = Sub()
Sub.__bases__
foo.__bases__
The last statement originates the following error:
This is an anomalous situation. Normally, if a class has an attribute,
instances have the same attribute (unless overriden). But this does not
matter.
That is not true: if a class has an attribute, you can not say its
instances have the same attribute. You can just say if a type defines an
attribute, all its instances have that attribute. Look at this example:
>>> class Foo(type):
... foo = 33
...
>>> Foo.foo
33
>>> MyClass = Foo('MyClass', (), {})
MyClass is an instance of Foo, so it must have the attribute foo:
>>> isinstance(MyClass, Foo)
True
>>> MyClass.foo
33
But an instance of MyClass is not an instance of Foo, and so MyClass()
must not have the attribute foo. In fact:
>>> m = MyClass()
>>> isinstance(m, Foo)
False
>>> m.foo
Traceback (most recent call last):
...
AttributeError: 'MyClass' object has no attribute 'foo'
--
Marco Buttu
--
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