class My[X](object): raises TypeError: Cannot create a consistent method resolution order

[sobolevn]

>>> class My[X](object): ...
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <generic parameters of My>
TypeError: Cannot create a consistent method resolution
order (MRO) for bases object, Generic

It looks like a correct error:

>>> from typing import Generic
>>> from typing import TypeVar
>>> T = TypeVar('T')
>>> class A(object, Generic[T]): ...
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Cannot create a consistent method resolution
order (MRO) for bases object, Generic

>>> class A(Generic[T], object): ...
... 
>>> 

But it is not tested. I think that object is quite an important corner-case to test it explicitly.

class My[X](): is tested.

Linked PRs

• gh-107909: Test explicit object base in PEP695 generic classes #108001
• [3.12] gh-107909: Test explicit object base in PEP695 generic classes (GH-108001) #108022

[brandonardenwalli]

Hi! I am to try to follow along, but I am not able to get the same error from the first example you give:

class My[X](object): ...

gives me

File "<stdin>", line 1
    class My[X](object): ...
            ^
SyntaxError: invalid syntax

the second example works for me though:

class A(object, Generic[T]): ...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Cannot create a consistent method resolution
order (MRO) for bases object, Generic

Am I doing something wrong? How to fix to reproduce the same error as you?

P.S. how to make code formatting look like your examples? I use the "Add code" button but my code looks different from yours in the preview.
Update for P.S.: see #107909 (comment)

[brandonardenwalli]

Okay, I run again after great suggestion from JelleZijlstra in other conversation. I can now reproduce:

>>> class My[X](object): ...
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <generic parameters of My>
TypeError: Cannot create a consistent method resolution
order (MRO) for bases object, Generic
>>> from typing import Generic
>>> from typing import TypeVar
>>> T = TypeVar('T')
>>> class A(object, Generic[T]): ...
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Cannot create a consistent method resolution
order (MRO) for bases object, Generic
>>> class A(Generic[T], object): ...
...

For anyone also stuck with same problem as me above, try to do #107905 (comment)

[AlexWaygood]

@brandonardenwalli, please use triple backticks to format multiline code blocks in GitHub issues, i.e.:

```
Your code here 
```