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stubtest: additional guidance on errors when runtime is object.__init__ #19733

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merged 1 commit into from
Sep 13, 2025
+23 −4
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stubtest: additional guidance on errors when runtime is object.__init__ #19733

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27 changes: 23 additions & 4 deletions mypy/stubtest.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1048,7 +1048,10 @@ def get_kind(arg_name: str) -> nodes.ArgKind:


def _verify_signature(
stub: Signature[nodes.Argument], runtime: Signature[inspect.Parameter], function_name: str
stub: Signature[nodes.Argument],
runtime: Signature[inspect.Parameter],
function_name: str,
warn_runtime_is_object_init: bool = False,
) -> Iterator[str]:
# Check positional arguments match up
for stub_arg, runtime_arg in zip(stub.pos, runtime.pos):
Expand Down Expand Up @@ -1093,6 +1096,8 @@ def _verify_signature(
msg = f'runtime does not have parameter "{stub_arg.variable.name}"'
if runtime.varkw is not None:
msg += ". Maybe you forgot to make it keyword-only in the stub?"
elif warn_runtime_is_object_init:
msg += ". You may need to write stubs for __new__ instead of __init__."
yield msg
else:
yield f'stub parameter "{stub_arg.variable.name}" is not keyword-only'
Expand Down Expand Up @@ -1132,7 +1137,11 @@ def _verify_signature(
if arg not in {runtime_arg.name for runtime_arg in runtime.pos[len(stub.pos) :]}:
yield f'runtime parameter "{arg}" is not keyword-only'
else:
yield f'runtime does not have parameter "{arg}"'
msg = f'runtime does not have parameter "{arg}"'
if warn_runtime_is_object_init:
msg += ". You may need to write stubs for __new__ instead of __init__."
yield msg

for arg in sorted(set(runtime.kwonly) - set(stub.kwonly)):
if arg in {stub_arg.variable.name for stub_arg in stub.pos}:
# Don't report this if we've reported it before
Expand Down Expand Up @@ -1218,7 +1227,12 @@ def verify_funcitem(
if not signature:
return

for message in _verify_signature(stub_sig, runtime_sig, function_name=stub.name):
for message in _verify_signature(
stub_sig,
runtime_sig,
function_name=stub.name,
warn_runtime_is_object_init=runtime is object.__init__,
):
yield Error(
object_path,
"is inconsistent, " + message,
Expand Down Expand Up @@ -1328,7 +1342,12 @@ def verify_overloadedfuncdef(
stub_sig = Signature.from_overloadedfuncdef(stub)
runtime_sig = Signature.from_inspect_signature(signature)

for message in _verify_signature(stub_sig, runtime_sig, function_name=stub.name):
for message in _verify_signature(
stub_sig,
runtime_sig,
function_name=stub.name,
warn_runtime_is_object_init=runtime is object.__init__,
):
# TODO: This is a little hacky, but the addition here is super useful
if "has a default value of type" in message:
message += (
Expand Down
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