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Metaclass conflict when combine class with a custom metaclass and str class #14818
Description
Bug Report
Mypy returns
error: Metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases
when I combine a class with a custom metaclass and a str class
To Reproduce
This works
class M1(type): pass
class A1(metaclass=M1): pass
class CorrectMeta(M1, type): pass
class B2(A1, int, metaclass=CorrectMeta): pass but this not - I only replaced int with str
class M1(type): pass
class A1(metaclass=M1): pass
class CorrectMeta(M1, type): pass
class B2(A1, str, metaclass=CorrectMeta): pass Expected Behavior
There is no error
Actual Behavior
Mypy returned an error
Your Environment
- Mypy version used: >=0.991
- Mypy command-line flags:
mypy -p mypackage - Mypy configuration options from
mypy.ini(and other config files):
[tool.mypy]
files = "**/**.py"
plugins = [
"pydantic.mypy"
]
ignore_missing_imports = false
scripts_are_modules = false
namespace_packages = true
disallow_untyped_defs = true
disallow_incomplete_defs = true
no_implicit_optional = true
show_error_context = true
show_traceback = true
strict_equality = true
check_untyped_defs = true
[tool.pydantic-mypy]
init_forbid_extra = true
init_typed = true
warn_required_dynamic_aliases = true
warn_untyped_fields = true
[[tool.mypy.overrides]]
module = [
"tests.*"
]
disallow_untyped_defs = false
disallow_incomplete_defs = false
[[tool.mypy.overrides]]
module = [
"request_session.*",
"sentry_sdk.*",
"structlog.*",
]
ignore_missing_imports = true
ignore_errors = true
- Python version used:
3.9, 3.10, 3.11
Activity
hauntsaninja commentedon Jun 20, 2025
#17713 makes this go away