On 04/11/2019 11:30, Veek M wrote:
1. Why do I get True whenever i tuple the
isinstance(f, (Bar, Foo))
(and why don't the print's run)
I'm not very familiar with metaclasses, but I can answer the second part
of your question.
The docs say that you can feed it a tuple and that the results are OR'd
----
The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
isinstance(x, A) or isinstance(x, B) or ... (etc.).
-----
which implies that the metaclasses are called for each class?
class MyzMeta(type):
def __instancecheck__(cls, other):
print('MyzzzzzzMeta', other)
return 0
class MyMeta(MyzMeta, object):
def __instancecheck__(cls, other):
print('MyMeta')
print(cls, other)
return 0
class Foo(list):
__metaclass__ = MyzMeta
pass
class Miaow(object):
pass
class Bar(Foo, Miaow):
__metaclass__ = MyMeta
pass
Aha. You're trying to fix up the metaclass after the fact, which is not
the right way to do it. If you change the class definitions to:
class Foo(list, metaclass=MyzMeta):
pass
class Bar(Foo, Miaow, metaclass=MyMeta):
pass
then you get the prints from MyMeta.__instancecheck__(). The
isinstance() still returns True, though, and I don't know why. Then
again, your definition of MyMeta is really weird.
f = Foo()
b = Bar()
print(isinstance(f, (Bar, Foo)))
--
Rhodri James *-* Kynesim Ltd
--
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