error: "type" has no attribute "from_private_key"

[rectalogic]

Bug Report
paramiko keys have base class PKey which has a classmethod from_private_key. When trying to call this on a subclass, mypy errors with:

error: "type" has no attribute "from_private_key"

To Reproduce

import io
from paramiko.dsskey import DSSKey
from paramiko.ecdsakey import ECDSAKey
from paramiko.ed25519key import Ed25519Key
from paramiko.rsakey import RSAKey

for pkey_class in (RSAKey, DSSKey, ECDSAKey, Ed25519Key):
    pkey_class.from_private_key(io.StringIO("hello"))

> python -m venv venv
> venv/bin/pip install mypy==1.5.1 paramiko==3.3.1 types-paramiko==3.3.0.0
> venv/bin/mypy pkey.py
pkey.py:8: error: "type" has no attribute "from_private_key"  [attr-defined]
Found 1 error in 1 file (checked 1 source file)

Actual Behavior

See above. Changing the code to this passes with no error:

import typing as ta
import io
from paramiko.pkey import PKey
from paramiko.dsskey import DSSKey
from paramiko.ecdsakey import ECDSAKey
from paramiko.ed25519key import Ed25519Key
from paramiko.rsakey import RSAKey

key_classes: ta.Sequence[type[PKey]] = (RSAKey, DSSKey, ECDSAKey, Ed25519Key)
for pkey_class in key_classes:
    pkey_class.from_private_key(io.StringIO("hello"))

Your Environment

• Mypy version used: 1.5.1
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.10.13

[JelleZijlstra]

At first sight this looks like another instance of topic-join-v-union Using join vs. using unions , but what's a little odd to me is that these classes have a common base, so shouldn't the join of the types be type[PKey], not type[Any]? It seems that mypy's join infers type for types with a common base that do not have the same constructor. Here's a self-contained example

class A:
    x: int

class B(A):
    def __init__(self, y: str) -> None: ...

class C(A):
    pass

for x in (B, C):
    reveal_type(x)  # Revealed type is "builtins.type"

I can see why that is (otherwise it would be unsafe to instantiate pkey_class), but it was surprising to me.

[hauntsaninja]

Fixed by #17408