[Python-Dev] Problems with mro for dual inheritance in C [Was: Problems with the Python Memory Manager]

Thu Nov 24 18:17:43 CET 2005

Armin Rigo wrote:
> Hi,
>> Ok, here is the reason for the leak...
>> There is in scipy a type called 'int32_arrtype' which inherits from both
> another scipy type called 'signedinteger_arrtype', and from 'int'.
> Obscure! This is not 100% officially allowed: you are inheriting from
> two C types. You're living dangerously!
>> Now in this case it mostly works as expected, because the parent scipy
> type has no field at all, so it's mostly like inheriting from both
> 'object' and 'int' -- which is allowed, or would be if the bases were
> written in the opposite order. But still, something confuses the
> fragile logic of typeobject.c. (I'll leave this bit to scipy people to
> debug :-)

Well, I'm stumped on this. Note the method resolution order for the new 
scalar array type (exactly as I would expect). Why doesn't the int32 
type inherit its tp_free from the early types first?
a = zeros(10)
type(a[0]).mro()
[<type 'int32_arrtype'>, <type 'signedinteger_arrtype'>, <type 
'integer_arrtype'>,
<type 'numeric_arrtype'>, <type 'generic_arrtype'>, <type 'int'>, <type 
'object'>]